Bitwarden uses the favicon from the first link in the password entry.
For my selfhosted web pages I use the public info page of the selfhosted page (e.g. openMediaVault) and set detection to [none].
This way it won’t match against the 3rd party page but I get the icon :)

BUUUT it should only poll if you activate the program/extension.
Don’t know why it should poll at midnight