Make debug messages more consistent

[Jachimo]

Debug messages should be consistent with Google Python Style best practices:
https://google.github.io/styleguide/pyguide.html#s3.10.1-logging

For logging functions that expect a pattern-string (with %-placeholders) as their first argument: Always call them with a string literal (not an f-string!) as their first argument with pattern-parameters as subsequent arguments. Some logging implementations collect the unexpanded pattern-string as a queryable field. It also prevents spending time rendering a message that no logger is configured to output.

[Jachimo]

Some improvements were already made in 0c61d3b