At first it appears as a bug of autosyncing, but tongle enabling FSRS helper addon gives the source of the problem …

Bug also submitted in FSRS Helper’s Github:

https://github.com/open-spaced-repetition/fsrs4anki-helper/issues/242

Error
An error occurred. Please start Anki while holding down the shift key, which will temporarily disable the add-ons you have installed.
If the issue only occurs when add-ons are enabled, please use the Tools > Add-ons menu item to disable some add-ons and restart Anki, repeating until you discover the add-on that is causing the problem.
When you’ve discovered the add-on that is causing the problem, please report the issue to the add-on author.
Debug info:
Anki 23.10 (c2b1ab5e) Python 3.9.15 Qt 6.5.0 PyQt 6.5.0
Platform: Linux-6.5.4-1-MANJARO-x86_64-with-glibc2.38
Flags: frz=False ao=True sv=3
Add-ons, last update check: 2023-09-21 16:34:38

Caught exception:
Traceback (most recent call last):
File “/home/chris/ankidev/qt/aqt/taskman.py”, line 138, in _on_closures_pending
closure()
File “/home/chris/ankidev/qt/aqt/taskman.py”, line 82, in
lambda future: self.run_on_main(lambda: on_done(future))
File “/home/chris/ankidev/qt/aqt/taskman.py”, line 102, in wrapped_done
on_done(fut)
File “/home/chris/ankidev/qt/aqt/sync.py”, line 100, in on_future_done
mw.col.db.begin()
File “/home/chris/ankidev/pylib/anki/dbproxy.py”, line 36, in begin
self._backend.db_begin()
File “/home/chris/ankidev/pylib/anki/_backend.py”, line 100, in db_begin
return self._db_command(dict(kind=”begin”))
File “/home/chris/ankidev/pylib/anki/_backend.py”, line 116, in _db_command
raise backend_exception_to_pylib(err)
anki.errors.DBError: DbError { info: “SqliteFailure(Error { code: Unknown, extended_code: 1 }, Some(\”cannot start a transaction within a transaction\”))”, kind: Other }