Time Machine encryption password
I have an encrypted external HD for my Mac. Despite many times requesting the saving of the password in Keychain it doesn't. To make matters more confusing sometimes on start-up I am asked for the password to unlock the HD so that Time Machine can start using it, sometimes it doesn't ask and sometimes if it asks and you do nothing after a period of time it starts without entering a password.
All other Keychain and Internet passwords work. I can find no evidence of a Time machine password in Keychain.
iMac 27″, macOS 10.15