Elixometer.clear_counter/1 is supposed to use configured Formatter
A default formatter Elixometer.Utils is called instead of a configured one:
https://github.com/pinterest/elixometer/blob/c4a886b52e405a52e749b799e2a27908d526ecf5/lib/elixometer.ex#L292
To fix, Elixometer.Utils should either expose the configured formatter, or implement clear_counter/1.
Exposing formatter is preferable, because there are often situations where an application may need to translate metric names between "Elixometer view" and "exometer view".
Is this related to https://github.com/pinterest/elixometer/pull/114#issuecomment-412920521?
Yes, this is the same issue as you reported in the comment. I didn't notice it, because #114 is closed.