The following was unrelated to this issue.
I had a similar problem with my Place tree and I believe it was related to having some circular references in the hierarchy.
There is a hack to change the Place Tree selector to a ‘flat’ rather than a ‘hierarchical’ mode. (Thanks again to @DaveSch !) Would you be willing to try that?
Note that the symptom went away when I migrated from Windows to Linux with the same data.