Are you sure that where you are checking is the output of the converter? I don't think of breakers on the output of the converter as that is often just direct connection to the battery for charging, therefore should always read the battery voltage?
If one is not sure it is the input/output question, I might guess that the problem is a run down battery to explain the 7 volt reading and then when the battery is getting charged it would explain the 14 as being from the charging.
If this is true, some reading on "surface charge" may help.
But there is a lot of guessing there due to not knowing what RV , etc. !!
2015 Winnebago Vista 31KE on 2014 chassis