Since the update 5.12.5 I have a problem with the Application Menu. I'm not using the default Application Launcher but the Application Menu, added from the default Widget list.
The problem is the Application Menu is displaying the wrong application in the selected category.

So for example, I'm hovering first over Multimedia, VLC is listed, so no problem, but when hovering to above to Internet, VLC is still listed instead of Falkon browser.
Also clicking on that application in the menu is opening the wrong application. This working visa versa, it's always remembering the first catagory and is displaying those application(s).

It's seems this problem occurs only when there is one item listed in the category, so in my case in Multimedia, Internet, System Settings and on some computers also Office.
If I go to a category with multiple listings no problem, if I go from a category with multiple listings to one with one listing no problem. But if I come from a category with one listing and going to a category with one listing, the application listed is the wrong one.

I have this behaviour on multiple installations, before Plasma 5.12.5 on KDE Neon I had no problem.

Looks very similar to viewtopic.php?f=66&t=152367, bug reported in https://bugs.kde.org/show_bug.cgi?id=394013

This looks indeed as the same issue, hope the fix will come soon as the bug has been reported yet.
Thanks for your reply airdrik