The plugin listing appears for a short time and then instantly disappears in 1.19.5.

If you go to /admin/extend/plugins#download, it appears like this:

There are no errors in the browser console.

I am seeing the same thing in our forum. It all started with installing the awards plugin (which never worked) and it all went downhill from there. Even removing the plugin does not seem to help. @Normando did you get to the bottom of this and how did you fix it?