I am currently running Piwigo 15.5.0 through a Raspberry Pi and am unable to upload photos into an album

I have tried
a) resetting user cache
b) using alternative albums

The error log gives:

[2025-05-31 17:44:52][exec=JmV0A4S4nz]  [INFO]  [getuserdata][exec_code=9469][user_id=2] needs user_cache to be rebuilt
[2025-05-31 17:44:52][exec=JmV0A4S4nz]  [INFO]  [generate_user_cache-u2][exec=8b02938d] starts now
[2025-05-31 17:44:52][exec=JmV0A4S4nz]  [INFO]  [generate_user_cache-u2][exec=8b02938d] wins the race and gets the token!
[2025-05-31 17:44:53][exec=JmV0A4S4nz]  [INFO]  [getuserdata][exec_code=9469][user_id=2] user_cache generated, executed in 0.152 s

I don't know if this is 15.5.0 specific as although I use Piwigo regularly, I haven't uploaded any photos for some time.

Any ideas?