see here
https://vborg.vbsupport.ru/showthread.php?t=154437
you must overwrite your new forum home page with the index.php from the latest version of vb. when updating your board you overwrite your forum templates with the new templates from vb. when doing this, because you've changed the directory of your forumhome to for instance forum.php this does not get overwriten with te new index.php so you must overwrite it manually using your ftp program!
fix was found on vb.com for those interested