Oh what a shame
I'm not sure what to suggest as pockets don't work for my heavy wetter. Perhaps try again with more boosting? I have FBs but no PBs, so can't say which would be better at dealing with night boosting I'm afraid. I tried various inserts with my FB and found that overboosting just made the legs gape so the problem was worse. Not sure if PBs would be better, but someone else will be able to advise no doubt!
I'm sure he didn't wee more because he's in cloth, so wouldn't worry about this being a setback. It's just that in dispo pull ups you won't have been able to tell very easily how much he actually was weeing. If anything, I would've thought cloth will encourage him to wee less as he'll have an awareness of being wet which he wouldn't have with a dispo.
Don't give up, I'm sure there's an answer!!