Promoting changes results in 500 error

Hey hey I'm trying to promote some changes from development to production workflow. We have 2 steps in the workflow: one In-App and a second one is email sending. I've updated several fields in both steps. In the Changes history tab I can see two changes for such single workflow. When I try to promote one of the changes - everything works as expected and in the production workflow I can see changes in both steps that I made. But when I try to promote the "second" change - it results in 500 Internal server error. It happened in two different separate workflows. I am not sure why we got two different changes and what to do to remove such hanging changes that we cannot promote