I am also experiencing this issue.
Symptoms: After about 20 Minutes.
A designer can navigate around with issues on modules not saving re-adding then ignoring these notifications. can re-apply then save.
In the above link from GitHub How can this session time be increased to over many hours or days.
In previous versions and the Ubuntu installation this does not happen. Only Experienced it with this Bitnami Stack.
I am not a Ruby/Rails or Redis expert.
usage: timespan = Setting.get('recently_logged_in_timespan', 30.days.to_s).to_i.seconds
Will this resolve the issue?
Last issue left before moving to production.