After an upgrade, our pluginManager page is completely un-usable.  There's no UI button, tabs, controls - just a spew of red text indicating all the plugins.

It's likely we didn't properly check all the plugins for compatibility as our Jenkins version was quite old before we set this one up.

It's failing on these pages:
Updates: /pluginManager/
Available: /pluginManager/available
Advanced: /pluginManager/advanced – partially works, see screenshot

It renders correctly on, and presumably I could uninstall plugins at least (or use cli to do that) :
pluginManager/installed

I have attached a screencap of this issue - Does anyone have suggestion of how to fix it?