uploaded photos not visible right after upload

[plegall]

Back in 2021 and version 12, Piwigo introduced the "lounge". It is buffer mecanism. See description on https://piwigo.org/release-12.0.0#technical_features :

Lounge
New background mechanism, the “lounge“, to bufferize photos during upload. This will avoid too many user cache rebuilds. To make it more understandable: the server load will be much lower on large galleries during photo upload. When saying "large galleries" we mean 100,000 photos and more.

When you upload a photo, it is not immediately visible in the gallery (not even in the administration) of Piwigo. The lounge must be emptied first. You can either wait (5 minutes by default, see Piwigo $conf['lounge_max_duration']) or force the publish by calling pwg.images.uploadCompleted.

Piwigo Remote Sync should call pwg.images.uploadCompleted at the end of uploads.