Yes my son is 3.2 as well!
That's good that your DS's receptive language is good, (yet I understand probably actually more frustrating for him if he understands, yet others aren't necessarily understanding him! X)
I personally would bring the signing back in, as if it's makaton I think so many of the signs are 'obvious' iyswim and therefore it can only 'aid' nursery staff in understanding your little man. And could you ask if any staff have attended a course, (as even if you know they haven't, it's a subtle hint that it would be helpful!)
Your son sounds to have done well picking signs up originally! I've been trying to sign about 1 per very short instruction (ie get your shoes, I'd sign shoes) for months, yet my son can do perhaps 3, but I suppose that goes hand in hand with struggling with the receptive side as well.
Can I ask if/ your son's behavior is affected?
I suspect my son has ASD and am pursuing this with the paediatrician (therefore there may be other reasons for this,) but my son currently can hit, scratch etc I'm sure it's mainly because he can't make himself known.
Xx