Cannot fast forward merge

Summary

After update from 9.2.5 to 9.3.2-ee we cannot merge through the Gitlab interface.

Steps to reproduce

Project settings -> Merge method -> Fast-forward merge

Create a branch and a merge Request

The rebase button is always displayed

Make some changes in the branch

The rebase button is always there even if the branch is up to date agains master.

The merge button is invisible.

What is the expected correct behavior?

A merge button should appear if the branch is up to date against master.

The rebase button should be invisible if the branch is up to date against master

Relevant logs and/or screenshots