Well done with the sleep training! That's awesome
WRT to your current issue, you've worked out exactly what you need to do.
Then after a week or so he started taking 40 minute naps. I would put him down a bit earlier to compensate. Then that would be a short nap. Then he would need a 3rd nap and bedtime got pushed up to compensate. He will not resettle in his crib. He's super smiley and ready to play.
Classic undertired naps. Best not to reduce A time at all after an UT nap, though you can reduce slightly (I'd suggest a max of 15mins, not 30mins though! - its a rare baby who needs that much less).
6 up9 nap10:30 up1:30 nap3 up6 bedtime
Really super routine for a 6-7mo. Not so flash for LO now...
6 up9:15 nap10:00 up12 screaming12:30 nap1 up3:30 nap4:30 up7 bedtime, miserable
So UT for the first nap off 3:15 A time. Not sure what the screaming is at 12noon - other than tiredness, it could be: hunger/thirst, frustration whilst trying new skill, discomfort/pain,
Then 12:30-1 nap - perhaps OT, perhaps overstimulation, perhaps pain, perhaps related to screaming - could be many different things and not worth reading too much into it unless you're getting this happening as a pattern.
Then 3:30-4:30 - another UT nap off a short A time.
7pm BT - misery can be from UT too - how would you feel if someone sent you to bed when you weren't tired? Its not always OT.
We know he can get through that 45min sleep cycle transition. At this stage, its worth trying 3:15 consistently for all A times for 3-4 days before trying to push the first A time to 3:30. Am I right in thinking the only time you've done 3:15 first off, you've then followed up with two A times of 2.5hr as above? If so, give the consistent A times a go as you have recently had good success with 3hr for all A times.
At this age, you're not necessarily going to get a 12hr night any more. 11hr is perfectly acceptable and reasonable at this age, so don't worry about the day running 6am-7pm.