Hi, I was just dealing with a similar issue in CACHE 2018.1.2 on Windows.  After enabling auditing and enabling LoginFailure audit events, I got the following from Event Details in the Audit Details:

 Error message: ERROR #5002: Cache error: <DIRECTORY>LOGIN+96^START *c:\intersystems\cache1\mgr\user\
Service name: %Service_Console
Login routine: Programmer mode
$I: |TRM|:|13108
$P: |TRM|:|13108

I had deleted my CACHE.DAT file from the directory with my User database. After copying that file from a backup to the right directory, I could login to the terminal again.