As a final update, i did remove every single forge microblock from one of the affected chunks and the block placing stutters are no longer there in that chunk.
In another chunk where i have still have microblocks the stutters are definitely there so to me that confirms it.
I further reinforces my suspicion that the once per second stutters was caused by those two chunks updating in unison AFTER i had placed a bunch of microblocks in them and then ran the crucibles in those chunks.
One of those chunks is my steel production setup where i use magnetite in two crucibles so in addition to the once a second stutters, i also had insane stutters when new magnetite was added to the crucibles (7 magnetite and 3 charcoal to be precise via hoppers dropping) which causes at least 10 updates to happen in succession which really messed up the game.
I’mma see if Optifine alleviates the issue… But i don’t trust optifine… I’ve had issues with it in the past.