Hi, I've the same problem as of about an hour or 2 ago on my Xperia z3, mouse suddenly stopped responding on my phone with AirMirror... the keyboard works fine, just the mouse from the PC is playing up. The only reason I was able to unlock my phone (broken touch screen) at all is because I connected the mouse directly to it... but the mouse not working is quite a problem otherwise!
Using v3.2.1 on phone, can't see the version of the PC app, does it show it anywhere? It says it's up to date, so I guess whatever the latest version is at the time of writing this. I'm reluctant to roll back to an older version as suggested above in case there's another problem and I can no longer access the phone at all, thankful to have any access at all right now! (a great app when it's working, thank you)
Also this problem occurred out of the blue, no updates, nothing. The only thing I can think of is that it's the 1st July, unless there's changes set to take effect as of today wherever in the world it just turned 1st July cpl hours ago, then it's strange for this bug to appear out of nowhere...