Indeed, I had a stall once in a melomel with just a few lemons in secondary. Not a big deal since it was secondary, and residual sweetness counterbalanced the tartness nicely. Got really quickly really clean though.
I would say using just the skins for flavor is much more feasible. Also I quarter citrus, slicing them like this is just asking for lots of mush at cost of laborous slicing.
So are you adding sugar this time or not?