P: Collections panel shows one collection after restarting LR with panel collapsed

The Collections panel shows just one collection after restarting LR with the panel collapsed.

To reproduce:

1. Select all All Photographs in a catalog with at least 1000 pics and a mix of at least 15 collections, smart collections, and collection sets.
 

2. Collapse the Collections panel.
 

3. Restart LR.
 

4. Expand the Collections panel and wait a second or two.
 

5. Collapse the panel, wait a second, expand the panel.
 

6. Observe that after a second or two, only the first item in the Collections panel is displayed.
 

See this screen recording:

https://www.dropbox.com/s/colwkzomf91eamd/collections-panel-bug.2020.10.20.mov?dl=0 

A workaround is to change the panel from Sort By Name to Sort By Kind, or vice versa, and then collapse and expand the panel.  Another workaround is to expand the panel and then restart LR.

Tested on two instances of LR 10.0 on Mac OS 10.15.5.  I can't reproduce this on Windows 10.  

One other person has also observed this:

https://www.lightroomqueen.com/community/threads/possible-plugin-issues-with-collections-in-lrc-10.41326/

He thought it might be related to plugins, but I disabled all my plugins in the recipe above.