Thanks for that. Confirmed SSH changes you mention above were the problem. To upgrade any other routers with my SSH configuration to 6.44.x I will first have to create a temporary remote access method to prevent being locked out. Another riskier option would be to add a script in scheduler that sets the correct SSH options at next startup, since they can’t be set in advance.
I agree that SSH forwarding-enabled might be better set to ‘both’ as a default, at least during upgrades, to prevent this type of problem.