I think our block-interaction code is using outdated semantics.
I've observed this with a little lag on Fabric, but I think the concept also holds on Forge.

We currently return SUCCESS in block activation callbacks on both sides, but SUCCESS will send out a hand-swing.
Vanilla follows this pattern:

• On the side that should trigger the hand-swing, return SUCCESS.
• On the other side, return CONSUME

There's a helper net.minecraft.util.ActionResultType#func_233537_a_, sadly unnamed, that is used by vanilla in this way:
return ActionResultType.func_233537_a_(world.isRemote) indicating it swings the hand on the client, but not again on the server.