[TYPO3] Inconsistent "Database error"

[Sebastian Holmqvist]

Hey. I just moved a 3.8.1 site to a fresh 4.0 (import from .t3d). Everything
works except from time to time I get "The current username, password or host
was not accepted when the connection to the database was attempted to be
established!" for no apperent reason. My service provider says they don't
see anything wrong, but something clearly is. The DB is on another host in
their setup, so I'm guessing some of the connection attempts don't reach
their target. How would I go about to get some more info in the error?
[SYS][systemLog] seems to fit my purpose but I couldn't make any sense of
the description.

Other ideas are also welcome.

Sincerely,

-- 
Sebastian Holmqvist