I wanted to move a Mechanical Saw and swap it with a Mechanical Chisel from Create Rechiseled, I tried many redstone builds, until I realized I had this in the modpack, but for some reason, the multipiston is unable to move either of those blocks, is there any way to fix that?

It'd really be a great feature.

Vanilla pistons are capable of moving this two blocks without issues, and I can even make a block swapper contraption for them, that does work, but it's two big and leaves the two block next to each other, which is an issue as one catches the blocks spewed by the other.

Why is the Multipiston not able to move them?

Vanilla pistons have some custom logic to allow piston movement. Some of this we could use to allow for modded block moving, but some is a lot harder, because we pull things through the block, so not only to the neighbor. So we can't easily re-use those events

I added a new tag: moveable_entity_blocks that you can try adding blocks to and see if they move correctly