I recently removed a couple of unused card types from my local database, which is forcing a full resync. When I choose to upload to AnkiWeb, it seems to upload successfully, but when the dialog changes to say it’s checking, I eventually receive a message that the connection timed out. The error details are empty. I am using version 2.1.60 on Linux; restarting has had no effect. Checking the database and media shows no issues.
I checked the connection timed out error page and tried mtr to ankiweb. It looks like I am seeing significant packet loss (~80%) from the second-to-last hop before anki’s network.
The last hop is most relevant. You could try increasing the timeout in the sync preferences to something larger, or try syncing on a different network in case it’s a temporary network problem.