6mo Ferber baby waking every hour after initial 7 hour stretch

Newly turned 6 month old. Ferbered for naps and sleep. Half-assed attempt at Ferber for MOTN wakes. Try to follow 5/3/3 for BFing. In own room. 2/2.5/2.5/3 schedule. Naps are 1.5/1.5/0.5. Wake time is 6:30am, bed time is usually around 8pm.

Baby has been doing well with his initial stretch and will usually sleep a solid 7 hours because waking up, usually around 4am. I feed him (not looking to night wean yet), no light, no interaction, and then pop him back into his crib. He's not necessarily fully awake, but not fully asleep either.

Without fail, he's then up an hour later. So today is was 5:20am after popping him back in at 4:20am. I ferbered this waking and he went back to sleep after a few minutes but I'm curious why he's immediately up an hour later and if there's anything I can do to stretch his second sleep to 6:30am.

Is it just a combination of low sleep pressure and a feed-sleep association still lingering at night?