Disable IPv6 in your router.
This bug should be solved a while ago but apparently isn’t.
.
No, but they will break. Uninstalling the app could make the devices being removed as well (not sure if zigbee just marks them as “unknown zigbee device”).
When you install the app again, you’ll possibly need to add the devices again, and repair the flows involved
Often installing an app without removing it first, works fine in case you try to fix things
