UM log in issue on multisite

I have a multisite. On my first site I use BuddyPress. On my second site I use Ultimate Member plugin which I have a little trouble with. UM plugin creates user accounts well, but when a user logs out from the site and tries to log in again, the plugin says that the user doesn’t exist in the base and denies to access into the site. I have checked this many times and the plugin does the same. Maybe I didn’t adjust the plugin properly. Please, help.