rspec:undercoverage job failing with Rugged:OdbError on MR

In the pipeline for an MR that adds a new feature spec, the rspec:undercoverage job is consistently failing with the following error:

`merge_base': object not found - no match for id (d2a508ffcc42b5e763b4564f3ae40abf32aab936) (Rugged::OdbError)

In the discussion, @toupeira mentioned that it might have to do with not squashing commits. (I've been doing it on Merge, but not rebasing locally)

Curious to hear thoughts!