https://pastebin.com/ZmwUmbNH

Server just crashed with the above. The setup that caused is:

Timer->redstone dust->AA atomic reconstructor->redstone dust->redstone repeater (4 ticks)->redstone repeater (4 ticks)->redstone dust->piston.

This is on the Undiscovered modpack.

And another one. After MCediting out the redstone, replacing everything. The moment redstone is placed down, server crashes.
https://pastebin.com/1dNwXQLp

Update: I believe this is related to trying to push (with a piston) a contentTweaker added block that is tool level 3 (obsidian level), at the same time it was being changed {(Via AA atomic reconstructor with mining lens) via redstone pulse.

This is the block in question:

var osmaticSteelOre = VanillaFactory.createBlock("osmaticsteelore", <blockmaterial:rock>); osmaticSteelOre.setToolLevel(3); osmaticSteelOre.setToolClass("pickaxe"); osmaticSteelOre.register();

It's the Piston. I see the issue. If there's no mobility flag set on the representation it breaks.

And the infinite loop is caused by the repeaters. I'm not sure if this is true everywhere, but in this modpack, if you place a piston down and power it against a block it can't move (e.g. obsidian), then remove the redstone, the redstone is still active, which feeds back into the repeater(s) and cause the loop, which crashes.