Calibre 9.4.0 crashes on macOS 26.3.1 when adding existing library

[sempaisan]

Hi everyone,

I’m running into a reproducible crash with the latest calibre 9.4.0 on macOS (Apple Silicon). The same library works perfectly fine when opened inside a Docker/Linux calibre instance, but crashes almost immediately on macOS when I try to add or open it.

**System:**
- calibre: 9.4.0 (official .dmg)
- macOS: 26.3.1 (25D2128) – Mac14,9 (M2 Pro or similar)
- Python (embedded): 3.14.2
- Qt: 6.10.x

**What happens:**
- I click “Library” → “Add library” → select my existing library folder
- calibre starts scanning/indexing the metadata.db
- Crash within seconds (EXC_CRASH / SIGABRT)

From the macOS crash report:
- malloc error: ___BUG_IN_CLIENT_OF_LIBMALLOC_POINTER_BEING_FREED_ WAS_NOT_ALLOCATED
- Key frames point to:
- sqlite3_load_extension
- apsw.Connection_load_extension
- libsystem_malloc abort

Full crash log attached (Fehlerbericht.txt)

**What works:**
- Brand new empty library on macOS → no crash
- The exact same library in Docker / Linux calibre → completely stable
- calibre 9.4.0 on macOS without touching the problematic library → runs fine

**What I already tried (no success):**
- Creating a "completely new" with an caliblre docker, after copying the ebooks to the new library and opening it on macos (during initial setup or first view) it crashes immediately.
- Starting calibre with --ignore-plugins


**Library details:**
- Created/used originally with calibre 8 on the same machine.
- ~1500 books (metadata.db size ~3,9 MB)
- No custom plugins installed in the macOS calibre


Has anyone else seen this with calibre 9.x on recent macOS versions?


Thanks a lot for any ideas or pointers!

Best regards,
Sempaisan

Attachments:
- Fehlerbericht.txt (the crash report)

[kovidgoyal]

See for example: https://bugs.launchpad.net/calibre/+bug/2139511