I have been trying to get the Nextcloud Gallery working and could not work out why it was just hanging.
What I had not realised is that under “Settings” you can see the log files for Nextcloud and right there are some very useful error messages.
I was getting an Allowed Memory Exhaused Error. A little googling pointed out that perhaps I had not allocated enough memory to PHP to allow it to work.
A quick check of the pool size showed I had allocated 128M. So decided as I have plently of memory to increase the size to 512M and see what happens.
Once NGINX restarted I was able to click on the Gallery and all of the folders appears with the thumbnail files.
So I then rechecked the log file and there we no errors any more.
Fixed.