In the latest update (r1.4-123), I've noticed the observers hold a strong redstone signal after a block update rather than just a pulse. We have a lightly modded vanilla server and use a lot of the double observer redstone trashcans as in the image included. The observer on the sticky piston holds a strong signal after completing the cycle.

https://imgur.com/WDMK3Qm

I reproduced the issue by creating a clean 1.12.2 Minecraft instance, added Quark r1.4-122. Tested a few times. Shut down the pack and updated to Quark r1.4-123 and tested again.

I get this issue too, using ilmango's universal tree farm (which has a world download link for testing) it fails on the third sapling placement. Removing Quark fixes it, also downgrading to Quark 1.3-117 fixes it.

I did some git bisecting and landed on this commit: 37d5488

For completeness' sake, my testing setup:

Poke the lever a bunch of times, and if any of the lights get stuck on, it's broken.