Hey there,
A few days ago, I updated to the latest version (13.0.0? 13.1.0 is showing on the Piwigo.org page as being available yesterday, but I didn't get to do that, for obvious reasons.), yesterday I tried moving a folder, and the following came up.

"
Warning:  [mysql error 1017] Can't find file: 'piwigo_user_cache' (errno: 2 - No such file or directory)

SELECT
    ui.*,
    uc.*,
    t.name AS theme_name
  FROM piwigo_user_infos AS ui
    LEFT JOIN piwigo_user_cache AS uc ON ui.user_id = uc.user_id
    LEFT JOIN piwigo_themes AS t ON t.id = ui.theme
  WHERE ui.user_id = 1
; in /var/www/g.mancavgeek.co.uk/html/include/dblayer/functions_mysqli.inc.php on line 847


Fatal error: Uncaught Error: Call to a member function fetch_assoc() on bool in /var/www/g.mancavgeek.co.uk/html/include/dblayer/functions_mysqli.inc.php:211 Stack trace: #0 /var/www/g.mancavgeek.co.uk/html/include/functions_user.inc.php(379): pwg_db_fetch_assoc() #1 /var/www/g.mancavgeek.co.uk/html/include/functions_user.inc.php(293): getuserdata() #2 /var/www/g.mancavgeek.co.uk/html/include/user.inc.php(76): build_user() #3 /var/www/g.mancavgeek.co.uk/html/include/common.inc.php(169): include('/var/www/g.manc...') #4 /var/www/g.mancavgeek.co.uk/html/index.php(11): include_once('/var/www/g.manc...') #5 {main} thrown in /var/www/g.mancavgeek.co.uk/html/include/dblayer/functions_mysqli.inc.php on line 211

"

It turns out the disk on my VPS was full, but even after freeing up several Gb of space (removing some test sites and deleting some videos from NextCloud), this error still exists.
PHPMyAdmin throws up an error

"
#1017 - Can't find file: 'piwigo_user_cache' (errno: 1 - No such file or directory)
"

on the table 'piwigo_user_cache', and a similar one on 'piwigo_user_cache_categories', and there are other errors on other tables that link to these.
Has anyone any clue as to what is happening here and how to fix it?
I've done a search, and while rare, this does happen occasionally, usually with a full disk, or while moving albums, and in every case either the poster says they fixed it without giving any indication of what they did, or there are no replies.

Thanks,
madbloke
Piwigo URL: https://g.mancavgeek.co.uk