Statamic 2 - problem with logging in, cache related

[sjankowski]

I have a problem with one Statamic 2 site i work on - sometimes it gets "blocked" so whoever tries to login to CP gets "These credentials are incorrect" response and can't login successfully. When i login via ssh and remove contents of cache folder - it works again.
It happens in very various intervals, sometimes it's once per month, sometimes it's multiple times in one day.

Seems like similar problem to one described here: https://statamic.com/forum/3780-caching-issue-with-logging-in-on-the-front-end but clearing cache every time it happens is not a really good solution for me, as few other people are working on this site and they are not familiar with clearing the cache without the access to CP...

Does anybody has any clues where i should look for the source of this problem? How to debug it next time it happens?
And finally how to fix it/prevent it from happening?

Thanks a lot for any advice!