Why is there no return for login after locking xubuntu session?

Question

Xubuntu

I recently installed xubuntu 17.04 and it seems to work tolerably well. After an indefinite number of screen locks in one of these locks, you simply cannot go back to entering the password, a stupidly black screen although the computer is working, and if you restart the computer, everything works fine as before before the eyes of the initial data entry window. There are no reactions to hot keys, any. This happens only after the session is locked on the computer (similar to Ctrl + L Windows).