Sounds like a similar issue as reported in this thread:
Maybe give this a try:
Also I’m curious if it’s related to libinput in some way. Could you try downgrading that one and see if that helps? edit Nah, forget that, it doesn’t help. Just tried on a VM.
edit2 Downgrading seatd seems to help though.
Now since downgrading is not really a good option (imho it should only be used to identify the package/source of the problem or when there’s really no other option currently) I would either go for:
a. Apply the workaround linked above
b. Switch to another DM (that’s probably the more sane one 
)