Single instance mode not working

[0xC4N1]

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Brief Summary

I used to launch KeePassXC to prompt for database unlock when no ssh keys are available for ssh authentication. On MacOS this used to work too but now it seems to ignore the single instance mode setting.

Unrelated to #12049 since my USER variable is letters only.

Steps to Reproduce

1. Download VirtualBuddy
2. Install the latest macOS recovery image
3. Upgrade to macOS 15.7.1
4. Install KeePassXC from keepassxc.org
5. Change system language to German
6. Launch and unlock the database
7. Enable single instance mode in application settings
8. Lock the database
9. Run /Applications/KeePassXC.app/Contents/MacOS/KeePassXC in terminal

Expected Versus Actual Behavior

It should prompt for database unlock in the same instance.
Instead it launches another instance of KeePassXC.

Error message in terminal:
The lock file could not be created. Single-instance mode disabled.
objc[14134]: Class AppKitImpl is implemented in both /Applications/KeePassXC.app/Contents/MacOS/KeePassXC (0x100cbc2f0) and /Applications/KeePassXC.app/Contents/PlugIns/libkeepassxc-autotype-cocoa.so (0x111ad02f0). This may cause spurious casting failures and mysterious crashes. One of the duplicates must be removed or renamed.
qt.qpa.fonts: Populating font family aliases took 53 ms. Replace uses of missing font family "Monospace" with one that exists to avoid this cost.

KeePassXC Debug Information

KeePassXC - Version 2.7.10
Revision: b342be4

Qt 5.15.11
Diagnosemodus ist deaktiviert.

Betriebssystem: macOS 15.7
CPU-Architektur: arm64
Kernel: darwin 24.6.0

Aktivierte Erweiterungen:
- Auto-Type
- Browser-Integration
- Passkeys
- SSH-Agent
- KeeShare
- YubiKey
- Schnelle Entsperrung

Kryptographische Bibliotheken:
- Botan 3.1.1

Operating System

macOS

Linux Desktop Environment

None

Linux Windowing System

None

[droidmonkey]

I cannot replicate this issue. Make sure you don't have two versions of KeePassXC installed (like a snapshot or custom build).

[0xC4N1]

I have updated the steps to reproduce this issue and added the error message from the terminal. The important difference seems to be that the system language needs to be something else than English. With an English system this issue does not occur and it stops happening once switched back to English.

[droidmonkey]

Still cannot reproduce with German as the system language. That should have absolutely no bearing on this anyway.

[phoerious]

Cannot reproduce either. Is this related? #12559