Having had this problem..
The resolution was...
I have an ohme charger.. all was good for two months until it cut its charge in half.
It comes with as CH clamp which had not been fitted.
What this does, is make sure that you will not blow the main fuse. IE if you have 60 amp fuse, and the system detects that you are within 7 amps of the Max, it will reduce the charging to only 3.6 kw.
However, I had a 100 amp fuse. So resolution was to tell the charger not too load balance, and all was well.
Why it worked ok for two months? Best guess is they did a firmware update, and the charger started to work as it should..
Hope that helps in some way..