"One work around I found is if I go to ROKU Live TV (not the tile but in the list on left of Home) then tune to a ROKU channel like 115 [...]"
Yes, this is also how I began the process that correlated with OTA channels returning to the channel guide, with internet connected.
"Once on an antenna channel TV doesn’t respond to back or return buttons - just home."
Have experienced this - have to get out of the antenna/Live TV selection, go back Home and then launch antenna/Live TV again; the TV usually becomes responsive to tuning OTA channels with remote, then.
When in a real mess, re-start TV - and if that doesn't work, unplug and 'reboot.' If that doesn't work... throw up your hands and say "&#$%."
It seems that many are experiencing variations of the problem, and it also seems that there is not a single solution that works for all. But, somehow, accessing the "Live TV" listing in left column does play a role, for some.
As mentioned, what also worked for me is to disconnect internet; of course, Roku TV isn't good for anything other than OTA, in that case... so that is not a "solution."
Best of luck.