Sugar maple partial leafing. What causes this?

[NamesakE]

I repotted a sugar maple last spring from the mix I originally put it in when I collected it (which was mostly pumice with some sphagnum moss and bark) to mostly akadama with some pumice. I conducted a major root pruning and put it in it's 1st training pot which is mostly screen. It struggled at 1st and looked like it wasn't going to make it but then I put a tank of heated water below it and it perked up and then made it all through last year doing really well. This year only a few branches are leafing out. I checked the other branches and the cambium is still alive so they're not dead. I'm black bagging it and hope it helps . Anyone have any ideas? I'd really appreciate it!

As a side note every year I've had this all the buds basically break at once. The three that have are really taking off but the others are doing nothing. I also pruned off a couple suckers at the base to keep the remaining trunks alive (this a raft style. I'm sure it's hard to see that from those pictures.