I had this problem and think I know fix so thought I would post here.
In the past, to backup I login to CPanel, click phpMyAdmin, and get logged right into that - - then take a DB dump (I do not trust only having a CPanel DB dump).
That has not been working lately and phpMyAdmin asks for a user/pass (the DB user/pass, not CPanel)
It turns out that whatever new version of phpMyAdmin is using now does not like CPanel passwords previously generated by CPanel due to special characters.
I changed CPanel password using a new CPanel generated password and phpMyAdmin likes it OK now. I only tried this so far on one site, but assuming this works for all.
Thought people would want to know.
While here, if anyone has latest-greatest way to auto backup mysql db (and perhaps files) to another remote location, please let me know. My manual backups to local are tedious.
Thanks,
Rick