What upgrade? WordPress core or Theme or any Plugin?
Support related to theme and/or plugins can be directly requested at their respective support forum.
Sorry, the WordPress upgrade.
I’ve made sure it wasn’t the plugins by disabling them all.
Have you tried:
– deactivating all plugins to see if this resolves the problem. If this works, re-activate the plugins one by one until you find the problematic plugin(s).
– switching to the default theme to rule out any theme-specific problems.
– resetting the plugins folder by FTP or PhpMyAdmin. Sometimes, an apparently inactive plugin can still cause problems.