Calibre start each second time with Traceback error

[MoritzSa]

Question / bug report

On a macOS installation of Calibre 6 or 7 (I tried both), I get each second start of Calibre the Traceback error. Then the library cannot be loaded and I have to close the Calibre application and restart it. At the second start Calibre opens. Also when I want to import a new ebook, I get a quite similar error each second time. Has anyone an idea what's happened?

Sorry for the partial German Log-Output, but I work with a German UI of my macOS.

Which version of Calibre are you running?

7.1.0

Which version of the DeDRM plugin are you running?

c.10.0.9

If applicable, which version of the Kindle software are you running?

no

Log output

calibre, version 7.1.0
FEHLER: Fehler beim Starten: There was an error during calibre startup. Parts of calibre may not function. Click "Show details" to learn more.

Traceback (most recent call last):
  File "calibre/gui2/main.py", line 316, in initialize_db_stage2
  File "calibre/gui2/main.py", line 259, in start_gui
  File "calibre/gui2/ui.py", line 365, in initialize
  File "calibre/gui2/tag_browser/ui.py", line 122, in init_tag_browser_mixin
  File "calibre/gui2/tag_browser/view.py", line 322, in set_database
  File "calibre/gui2/tag_browser/model.py", line 425, in set_database
  File "calibre/db/cache.py", line 88, in call_func_with_lock
  File "calibre/db/cache.py", line 1066, in set_pref
  File "calibre/db/backend.py", line 149, in set
  File "calibre/db/backend.py", line 134, in __setitem__
apsw.ConnectionClosedError: The connection has been closed

[ElleKayEm]

Since this is a calibre issue, ask over at the Mobileread calibre forum.