Being unable to use skills while lvl synched

[Felis]

Is there a reason I cant turn on Cleric Stance as a Scholar when the lvl synch put me to 36?

Yes
Because you have it in a cross-skill slot that is locked before 36. Put it in the first slot and you would have it even in Sastasha.

[Ghishlain]

Yes
Because you have it in a cross-skill slot that is locked before 36. Put it in the first slot and you would have it even in Sastasha.

Just to add a little more to this - you have access to one cross-skill slot at level 1 and get one every ten levels starting at 20.

1 Cross-Class @ level 1
2 Cross-Class @ level 20
3 Cross-Class @ level 30
4 Cross-Class @ level 40
5 Cross-Class @ level 50

If this trend continues, we'll probably gain one more cross-class ability at level 60.

As Felis has rightfully indicated, your Cleric's Stance is probably on the 4th or 5th slot, thus locking it out when synced to 36.