After upgrading to the newest version of lime survey, I've encountered problems with my surveys. Once I have loaded the participants table from csv file, my system slows. The slowness is happening in the survey settings but not in the survey list or the survey itself. The more participants I add the slower system becomes, first slowing down I've noticed was for about 5k loaded participants.

For my largest survey of about 40k participants not only does it take 15+ seconds to load any option (while loading the screen appears grey, see attached file Slowness_appearance), but also in some cases trying to send invites or reminders to the participants shows no response and reloading page throws error (see attached file Error1). Trying to expand number of participants per page at the bottom right of the site works only for about maximum of 250 participants per page (Chrome) or 2500 participants per page (Microsoft Edge) if I try to show more it throws an error as well (see attached file Error2).

The problem exists both for surveys created before and after the update and regardless of size or complexity of the survey. The only thing that seems to affect the speed of response is the number of participants.

Problem was tested both for csv files with only the obligatory attributes (firstname, lastname, email) as well for files with additonal attributes - both cause the error.

Clearing cookies or waiting for the system to "catch up" did not help with the speed - only removing the participants table did.

Integrity check did not show any problems with participants table.