Sync failure after Clear Unused Tags from Browse window

Open Anki.
Click Sync. (works ok)

Click Browse.
Click menu Notes → Clear Unused Tags.
Close Browse window.
Click Sync. (see ERROR message below)

A network error occurred.
Error details: error sending request for url(): connection error: bad protocol version

debug info:

Anki 2.1.44 (b2b3275f) Python 3.8.6 Qt 5.14.2 PyQt 5.14.2
Platform: Mac 10.16 (macOS Big Sur 11.3.1)
Flags: frz=True ao=True sv=2
Add-ons, last update check: 2021-05-28 19:19:28    

===Add-ons (active)===
(add-on provided name [Add-on folder, installed at, version, is config changed])
AMBOSS add-on ['0amboss_addon', 2021-03-04T07:41, 'None', '']
Batch Editing ['291119185', 2019-10-10T10:31, 'None', '']
Enhance main window ['877182321', 2020-12-22T23:42, 'None', '']
Frozen Fields ['516643804', 2020-02-29T23:12, 'None', '']
Image Occlusion Enhanced for Anki 21 alpha ['1374772155', 2020-04-27T22:21, 'None', '']
Picmonic Anki Add-On ['40737180', 2021-05-04T19:15, 'None', mod]
Pop-up Dictionary beta ['153625306', 2019-07-05T07:57, 'None', '']
Review Heatmap ['review_heatmap', 2018-10-28T18:06, 'None', '']
Special Fields ['1102281552', 2021-02-13T17:52, 'None', '']

===IDs of active AnkiWeb add-ons===
1102281552 1374772155 153625306 291119185 40737180 516643804 877182321

===Add-ons (inactive)===
(add-on provided name [Add-on folder, installed at, version, is config changed])

Thank you

That error seems unrelated, and looks more like temporary network issues, or something like a firewall running on your machine.

Thank you for your response. However, I can consistently recreate the problem many times (Sync failure after Clear Unused Tags).

I am not sure its a network issue because I can recreate the problem across different network environments.

I am not sure its a firewall problem because I am just using the MacOS (Big Sur 11.4) default firewall settings.

Also, Sync is always successful before I execute Clear Unused Tags.

Any other suggestions on how to debug this problem please?

I am not able to reproduce the problem here. If you can reproduce it without any add-ons, please see if you still get the issue using the latest alpha version in the beta testing section of these forums.

FYI, the problem no longer occurs after upgrading to macOS Big Sur 11.5.1 (and Anki 2.1.45). Thanks.

Hello, may I ask that you anonymize (or delete) this account please?

All done