Currently, I am running the newest anki version on mac. I have a M5 mac air and as a result, downloaded the mac) 13+ apple silicon version(26.05). Whenever I try to sync, it gives the message “Please use the Check Database function, then sync again. If problems persist, please force a one-way sync in the preferences screen.” When I do follow instructions, it gives a prompt to either upload to anki web, or download from anki web. Both of which works and allows sync “Database rebuilt and optimized”. However, my next sync again requires the same prompt “Please use the Check Database function then sync again. If problems persist, please force a full sync in the preferences section.” I have tried switching profiles, deleting the anki application and all its backups and or resources from computer, deleting my profile and making a new one, deleting all of my cards, and deleting all add-ons, and making sure Anki has permisions to full disk access. It is weird because on my windows laptop, everything works perfectly fine, with add-ons and anking decks and everything. I just don’t understand why the mac doesn’t.
Were you previously running Anki on this M5 MacBook Air without any problem, before installing Anki 26.05? That is, did the Anki version update cause the problem to start? If so, what version of Anki were you running previously?
Is your Windows laptop also running Anki 26.05?
Although it sounds like you’ve already tried a lot of these, please try all the other regular Troubleshooting Steps you haven’t tried already, to see if any of them might help.
I note that there have been previous issues like this in the past, but I don’t know if the previous causes are still relevant:
Hi,
Thank you for the quick response. I was previously running an older version of Anki on the M5 MacBook Air; I am not sure what version, though(probably the version that was on the main Anki page before)re 26.05 became the new standard). And then I started getting the repeating “please use the check database function, then sync again. If problems persist, please force a full sync in the preferences screen.” As a result, I deleted that version of Anki and installed the newest one (26.05). And it kept doing that. My Windows laptop is currently running Anki 26.05(in the help → about anki menu). I did all the regular troubleshooting steps and it doesn’t help. I did read the “Every sync must be a forced sync” forum and tried all the results suggested. The one I didn’t was using a “forced-sync add on.”
Here is a more specific description of what happens when I click sync on the M5 MacBook Air:
Click sync → “please use the check database function, then sync again. If problems persist, please force a full sync in the preferences screen.” → I do that → "There is a conflict between decks on this device and AnkiWeb. You must choose which version to keep:
- Select Download from AnkiWeb to replace decks here with AnkiWeb’s version. You will lose any changes you made on this device since your last sync.
- Select Upload to AnkiWeb to overwrite AnkiWeb’s versions with decks from this device, and delete any changes on AnkiWeb.
Once the conflict is resolved, syncing will work as usual." → If I click “Upload to AnkiWeb” → pop up “Uploading to AnkiWeb..” → pop up “checking” → pop up “processing” → pop up “Please use the Check Database function, then sync again. If problems persist, please force a one-way sync in the preferences screen.” → click ok → pop up “Please use the Check Database function, then sync again. If problems persist, please force a one-way sync in the preferences screen.” → The weird thing is, after all this is done, and I do check AnkiWeb, it did indeed upload the changes(ie. I did 3 cards, 3 cards were gone from new on ankiweb) → However, on the M5 MacBook Air, it still has a blue sync button(meaning changes aren’t saved) ??? which is weird → If I try clicking the blue sync button → pop up “Please use the Check Database function, then sync again. If problems persist, please force a one-way sync in the preferences screen.” → and it loops all over again
Backing up, if I instead clicked “Download from AnkiWeb” (ex. I added a new card) → click “sync” → "There is a conflict between decks on this device and AnkiWeb. You must choose which version to keep:
- Select Download from AnkiWeb to replace decks here with AnkiWeb’s version. You will lose any changes you made on this device since your last sync.
- Select Upload to AnkiWeb to overwrite AnkiWeb’s versions with decks from this device, and delete any changes on AnkiWeb." -.> I click download from AnkiWeb → pop up “Checking…” → pop up “Please use the Check Database function, then sync again. If problems persist, please force a one-way sync in the preferences screen.” → click ok → pop up “Please use the Check Database function, then sync again. If problems persist, please force a one-way sync in the preferences screen.” → and again, sync button is blue still, BUT the changes did save (ex. previously added a card on anki web, did the instructions above, and new card did show, but sync button is still blue → I click sync again → pop up “Please use the Check Database function, then sync again. If problems persist, please force a one-way sync in the preferences screen.” → and again, it is a loop, similar to if I tried the upload to ankiweb route.
And again: my email account is fresh(I removed my account via AnkiWeb → Account successfully removed), I have a fresh Anki Profile(ie. no cards or history), I deleted all previous Anki folders and files before fresh installing a new one, no Add-ons, I have tried backing up cards, and importing to new profiles → no work 
I also want to mention that I have an iPhone with the Anki app as well, and it syncs perfectly fine, the version is 25.09(settings → about).
So, it seems that:
- The problem previously started with some older version, and updating to 26.05 did not fix the issue.
- The issue is that, when asked to sync, the Mac desktop Anki app believes that there is something wrong with the database.
- Running Check Database and then a forced upload sync seems to perform the sync just fine. However, it doesn’t eliminate the issue. Anki still believes that there is something wrong with the database.
- Profile switch and profile deletion didn’t help.
- Deleting and re-installing the Anki app didn’t help.
- Deleting the collection didn’t help.
- The Windows desktop Anki app does not see any issue with your collection.
- The AnkiMobile app does not see any issue with your collection.
During your troubleshooting, did you ever delete or move/rename the Anki2 directory? (~/Library/Application Support/Anki2)
I’m thinking of a scenario where the Anki2/prefs21.db file might get corrupted in such a way that Check Database is unable to fix the issue. I’m thinking that by moving/renaming the existing Anki2 directory, when Anki is next run it will believe it is being run for the very first time and will create the Anki2 directory and prefs21.db file. The new prefs21.db file should be uncorrupted.
I’m hoping that someone with more experience with this might chime in whether this line of troubleshooting is valid? (Or, perhaps prefs21.db holds only profile information, so it shouldn’t be related to the problem?)
(Your collection, media files, add-ons, backups, etc. are in the Anki2 directory. After Anki creates the new Anki2 directory, you should be able to download your collection and media files from AnkiWeb to recover them. And if you simply move/rename the directory from Anki2 to some other name, you can always undo things and get back to the current state by simply moving/renaming it back.)
Yes, when trying to troubleshoot the issue, I did touch the Anki2 directory. I tried deleting it when deleting all of Anki and retrying once. I also tried to rename it once to Anki2_old. That didn’t work either. Currently It is just Anki2. Do you recommend I try to rename it? or move it?
If you already deleted it once and renamed it once, then I don’t think doing any of those activities again will help. (But, if you do, I recommend just renaming the directory.)
I’m at a loss about what else can be tried.
When you say renaming the directory, what do you mean? Should I rename Anki2 to something else?
Yes, rename it like you did before, to something like “Anki2_old2” (so you can rename it back to “Anki2” if you ever want to undo the change).