And in this image I have Collections selected; no change.
I have verified this issue exists both in Chrome & MS Edge, so this is not a browser specific issue. I have also verified that the collections feature DOES work in Both Android & iOS apps. And yes, Collections is enabled for this library.
Server Version#: 1.32.1.6999
Player Version#: Plex Web 4.100.1
<If providing server logs please do NOT turn on verbose logging, only debug logging should be enabled>
The Big Hammer option that usually fixes things like this is to use Restore Defaults under Settings > Plex Web > Debug (you have to have ‘Show Advanced’ enabled).