Hi there, found your post!
Just popping on as requested with some support.
Could you post the routine for us - WU time, what time you try for naps (and when he sleeps in the buggy) and what time bedtime is? I believe he is an independent sleeper at bedtime, is that right?
Without seeing the routine I would say that this is probably a phase, the run up to birthdays always seems to cause chaos
But that also you may need to make some changes such as pushing the nap later to avoid resistance, and possibly needing to do some WIWO or similar to get him back to sleeping in bed.
Will wait for your routine x