Mail app on macOS repeatedly asks for SMTP

Latest MacOS, M4 Mac mini.

I have my own domain managed by Apple since 2022 and all has been working great. I also use "Hide My Email" pretty extensively with no issues.

Recently (past 2-3weeks) some times I reply to a message that has an HME address, it asks for the outgoing SMTP server to use. I always use iCloud and select the option to "always use this server". This is the only SMTP server that I have had configured for a long time (years). Yet each time it asks again what server to use. This is getting annoying.