We have mongo users and Authentication Database that are like 000010 (numbers with leading 0).  We see in mongo log that compass translate the Authentication Database string in number (in the example 000010 string become 10 number). So the uthentication fail.

Example of log row with error:

2018-08-29T09:23:29.522+0200 I ACCESS [conn50898035] SCRAM-SHA-1 authentication failed for 008373 on 8373 from client 192.168.15.66:30464 ; UserNotFound: User "008373@8373" not found

The Authentication Database is not 8373 but 008373. The string is converted to number.