On Apr 5, 2021, at 2:47 PM, Stefan Monnier <monnier@iro.umontreal.ca> wrote:

The problem above is easy to workaround until the problem is fixed
upstream

Yes a simple ‘(cursor-intangible t rear-nonsticky nil) seems to do it. 

I'd tend to suspect an interaction with some wild-west
package doing dangerous things)

Your suspicions are well-calibrated.  I haven’t yet figured out the culprit, but it was a package interaction issue.