Anthony Rinaldi

My issue was in a world that started in 1.14.4.

Thanks for all the info! Deleting the entries from the chunk did fix the problem. 

The issue did happen to my when I died, however I dismissed it because I was killed by a player who stayed in the area and loaded the chunks for a while before and after I died. This other player also confirmed that the flying machines were all working properly after killing me, before logging off the server. Perhaps it's an issue with chunks in the vicinity of a dead player who has yet to respawn? I'm trying to replicate now it in single player and multi player by staying on the death screen for a while after dying near various redstone circuits and tile entities across different chunk border configurations, but even after many rounds of waiting with high tick speeds, I have yet to replicate it. 

As of 1.14, all blocks other than air raise the max height of any particular (x, z) coordinate. Every slime spawn attempt at a particular (x, z) coordinate is distributed from bedrock to the corresponding max height. In previous versions, blocks like water and glass didn't raise the max height, so you could simply bomb a little hole in the bottom of the ocean and cover the top with glass to make a slime farm. Now in 1.14, you need to remove every block above the farm to get the same rates as previously.

It also helps significantly to dig out an area about 20 blocks out from your slime farm (as well as all blocks above this larger area), as this drastically increases the chance that spawn attempts will start in adjacent chunks and make their way to your slime chunk due to how pack spawning works.

Here's a google drive link to the zipped world folder: https://drive.google.com/open?id=1j0nac0qWlOkMg-DFuhjRgrLlUk_upBJk

I've torn apart the flying machines themselves to highlight the actual issue: the observers marked with polished granite don't fire when supplied with block updates.

The chunks of the witch farm were reloaded, and I've experienced that kind of breakage many times before. In that case, simply rebuilding the flying machines has fixed the problem. This breakage seems very different though, as now even without a flying machine, these observers cease to work.