Rubocop doesn't seem to take advantage of its cache anymore

As can be seen in https://app.periscopedata.com/app/gitlab/652085/Engineering-Productivity---Pipeline-Build-Durations?widget=8813172&udv=1005715

Rubocop takes a long time to run since 2020-08-17, as if the cache wasn't used anymore, somehow. The timing got even worse on 2020-11-06 (this one seems to coincide with 07257f8b).