Yeah, I must admit I don’t get as much use out of either this or Ableton in general as I’d like to (seem to be getting motivated just now which is good). Don’t recall having many issues with TouchAble 3 previously, upgraded to Pro several months ago but haven’t really used it much until yesterday.
I use a 2011 iMac mostly for music (as well as external display for my laptop), on macos 10.12 & Live 10.
I tend to leave Ableton running, and often just wake up the machine enough that I can play piano on an always-armed instance of Pianoteq, but I have an iPad on the music stand so that I can look at sheet music / use TouchAble to do Ableton stuff when I’m in that mode.
For me it seems that restarting Ableton is fairly reliably getting the connection working again. So not at all the end of the world, and actually on reflection that might help to encourage me to actually do a bit more of the other bits of music-making I’ve tended to neglect. However, I don’t think it’s just when waking from sleep - pretty sure it randomly lost connection in the middle of a session yesterday when I’d really prefer to just stay in the mode of recording / playing / tweaking a few things with the iPad, and like not to have to move in front of the computer at all, let alone for troubleshooting tech issues. Ho hum.
Looking at my log, I see (clipped at an arbitrary point before errors)
<<<.... lots of general activity while things were working ....>>>
2021-03-04 18:26:39 [1414025796] INFO Argument 1: STRING 8
2021-03-04 18:26:39 [1414025796] INFO OSC MESSAGE WITH PATTERN BEGAN:: /script/load/end
2021-03-04 18:26:39 [1414025796] INFO OSC MESSAGE WITH PATTERN BEGAN:: /scene
2021-03-04 18:26:39 [1414025796] INFO Argument 1: STRING 1
2021-03-04 18:27:31 [1414025796] INFO OSC MESSAGE WITH PATTERN BEGAN:: /track/current_monitoring_state
2021-03-04 18:28:43 [1414025796] DEBUG wait for received failed to select with to socket 26 wit error (null)
2021-03-04 18:28:43 [1414025796] DEBUG Successfully connected to script TCP port on port 9009
2021-03-04 18:28:45 [1414025796] DEBUG wait for received failed to select with to socket 26 wit error (null)
2021-03-04 18:29:11 [1414025796] DEBUG failed to connect to port 9009 wit error Operation timed out
2021-03-04 18:29:38 [1414025796] DEBUG failed to connect to port 9009 wit error Operation timed out
2021-03-04 18:30:04 [1414025796] DEBUG failed to connect to port 9009 wit error Operation timed out
2021-03-04 18:30:30 [1414025796] DEBUG failed to connect to port 9009 wit error Operation timed out
2021-03-04 18:30:30 [1414025796] DEBUG failed to connect to port 9010 wit error Connection refused
2021-03-04 18:30:30 [1414025796] DEBUG failed to connect to port 9010 wit error Connection refused
<<<lots of oscillation between connection refused / operation timed out on various different ports>>>
Actually, as I look at it now (10:00), the last message in the log is an “Operation timed out” at 9:40, even though I have since then restarted Ableton and it is now connected and I’ve done a few interactions.
Anyway, I’d like the experience of this to be a bit more Zerodebug 
When I feel like debugging, I’ve got my own software for that…
Still, my pain is certainly much less than anyone who actually can’t get it to connect at all.