Big Problem Dolphin 7.3.5 Website

have a big problem for a few days.

every night when normal people lie in bed and sleep,

on my Dolphin 7.3.5 page several accounts of the members are deleted,

Last night, six member accounts are deleted.

I had turned off the site last night but accounts are being deleted overnight.

This is already several days.

Have tested with two virus programs unsuccessful.

No virus.

Someone must have access to the database.

there is no other explanation, Or?

Is it a problem to give people the Dolphin PHP database access,

To look for problems?

I had already tried to change the database name, but there are problems.

I have Plesk with Ubuntu 16.4

Passwords are changed regularly. In Panel.ini, I restricted access to Plesk.

No abnormalities can be found in the Dolphin website logs

Every morning I have to restore the Dolphin site with Restore.

My other Dolpin and Joomal websites have no problems

You may have pruning turned on for accounts that have not logged in for X number of days.  Go to Admin, Advance settings and then expand the Pruning section.  Look for Delete profiles of members that didn't login for; enter a zero (0) to turn off pruning of profiles.  If you are backing up your database, you might can retrieve the deleted profiles.

Yes, unfortunately I have overlooked.

Thank you for your tip