There are probably a couple of things going on here.
1) the voltage you saw was *NOT* float voltage. It was voltage with the fridge and water heater control boards pulling some power, the propane detector pulling a little power, lights and anything else that was active on the
12v side pulling a bit of load. That's going to result in a lower voltage reading than the "float" voltage that'll give you a guesstimate of state-of-charge. You'd need to let the batteries sit with zero load for a bit to get a real float voltage.
2) (this is a guess) your battery manager may be correcting somewhat for that portion of battery capacity you really shouldn't use. Pulling all the amp-hours the battery will supply before
12v devices don't have enough voltage to operate property really shortens battery life, even for AGMs, so the Victron may be reading usable capacity instead of total. I don't have one of these thingos (it's on the upgrades list) so I don't know exactly how it computes the capacity it's displaying, again that's just a guess.