Wrong number of Merge Requests

Summary

It happened to several projects of ours with GitLab Enterprise Edition 12.3.2-ee and also earlier, that the number of Merge Requests showing on the left navigation bar doesn't match the actual number of open MRs, until a new MR is created.

Steps to reproduce

After merging some MRs, check the number on the left nav bar.

What is the current bug behavior?

The Merge Requests row on the left navigation bar shows the wrong number of open MRs.

What is the expected correct behavior?

The Merge Requests row on the left navigation bar shows the actual number of open MRs.

Relevant logs and/or screenshots