Too many event actions causes error in visitor log and visitors widget


Ever since a website of ours started to track lots of event actions, we started to get the “Oops… there was a problem…” error on Visitors in Real-time widget and on Visitors -> Visitor log page.
In the Visits Overview Page (which also sometimes getting the error) we can see there are 6K actions per visit with 80 visits per day, and 400K max actions in one visit.

We cant find any errors in the log file, nor in the nginx log file.
Is there any other way to find the source of the problem? Is it possible too much data error?

Our Matomo instance is running on Openshift.

Thank you