I have set PARSE_SERVER_CLEANUP_INVALID_INSTALLATIONS: 0 in my heroku config.
However I do see it removes device tokens in the logs:
2018-04-12T13:58:37.911121+00:00 app[web.1]: info: Removing device tokens on 1 _Installations
I run parse-server 2.7.4.
I did have a look at the code checking the config value and it looks correct in my eyes. I do not know whats going wrong.