I have auto-save enabled in KeePassXC.
When I shut down my computer, the program will receive the termination signal and close.
When I shut down my computer, my OS informs me that KeePassXC is preventing the shutdown from completing.
KeePassXC - 2.2.0
Revision: caa49a8ef3ee28ed478192389b21d61107b3b8e0
Libraries:
Operating system: Windows 10 (10.0)
CPU architecture: x86_64
Kernel: winnt 10.0.15063
Enabled extensions:
I have not personally experienced this issue. Are you storing your database on a cloud service by chance?
I can reproduce it on macOS:

Maybe related to #580? ping @phoerious
I suspect that it only occurs when a change or addition has been made. I can confirm that pressing the save button (which is redundant given the autosave option) does not free up the shutdown-blocking state, but closing the database does.
I have this happen under KDE on Arch Linux. KDE will hang on shutdown stating that KeepassXC is preventing it from shutting down. If I issue a second shutdown command, it will shut down. This is KDE behavior, but I don't know why it's targeting KeepassXC. I can confirm this happens whether or not there are pending changes in KeepassXC.
Seeing this on Fedora 26 with Plasma.
Same on Gentoo & Plasma 5.11.4
This may happen if application ignores closeEvent for main window for no good reason
I've got the same issue using the plasma desktop in debian stable.
The message in .xsession-errors states:
ksmserver: Client "/usr/bin/keepassxc" ( 10c1bcb862000152058065200000015090010 ) canceled shutdown.
This bug is back for me since the 2.4.0 update!
Please open a new issue with all of your system details from the KPXC About -> Debug page.
Most helpful comment
I have this happen under KDE on Arch Linux. KDE will hang on shutdown stating that KeepassXC is preventing it from shutting down. If I issue a second shutdown command, it will shut down. This is KDE behavior, but I don't know why it's targeting KeepassXC. I can confirm this happens whether or not there are pending changes in KeepassXC.