Remote user blocked from mouse control

I'm using TeamViewer v12 on Ubuntu and for some reason, when someone tries to connect to a presentation I've started, and I click beside their names in the TeamViewer presentation window, they can't use the mouse. Their clicks don't work, and I don't see the mouse pointer moving on my system. These people don't have any problems like that when connecting to other systems.

I don't think this is the same problem as https://community.teamviewer.com/t5/TeamViewer-General/Mouse-Clicks-Not-Working/m-p/12470#M6856 since both the host and client system lose mouse control there. My host system retains control.

We're all using Ubuntu. I've tried doing things like changing my video driver and "Improve application compatibility". They don't make a difference.

Something interesting, that might be releated, is that for the most part, the client system does not display my mouse pointer. However, I have ssh'd into another sytem, w/X11 forwarding, and opened another window through that. They are able to see my mouse pointer when it hovers over the X11-forwarded window, although they can't move it.