Built this mob grinder yesterday and since then it hasn't spawned any mobs, it is also built on a floating island I made and I'm wondering if that may affect it, if it's not that or the newer version being a bit buggy, I don't know what the problem may be.
Difficulty is set to Normal, Y axis is 196 and my render distance is 32, the torches are only there so you can see the photo.
I afk'd over night 24 blocks away so it should work, no mobs spawn at all, it's not that they spawn and not fall down the water, they just don't spawn at all.
The last picture is indeed the top of the island in the first picture, and the two middle pictures is what is inside the stone brick box in the last picture.
I am playing on the recently released 1.14 and I am playing on a server with a friend and we've both tried leaving and reconnecting and only having one person on to see if that works but nothing seems to fix it.
The pictured design has some inherent inefficiencies due to being based on mobs wandering off the spawn platforms (rather than some form of active collection).
The cheapest improvemnet would be to lower the water streams (or raise the spawn pads) by 1 and line the edges with open trapdoors (which mob AI perceives as walkable).
Using smaller platforms (and more water streams, ideally including around the outside to prevent spiders climbing the walls) would also help, but be more work.
Moving to active mob collection (eg by using a clock to retract pistons releasing water that pushed the mobs into the drop) would be more effective still, but moves considerably beyond the early game design pictured,
Changes to the mob spawning algorithm in 1.13 distrubted the potential spawn attempt linearly over the blocks up to the highest (non-transparant) block in the xz-column selected [1.14 changed this to simply the highest block with a surface, but the 1.13>1.14 change is not applicable to the pictured design].
Placing the farm (actually the highest block above the farm) so high will result in fewer spawn attempts occuring on valid blocks although the percentage change in spawning from 1.12 should be small given builds at the same height.
If "playing on the recently released 1.14" means 1.14.0, there are a number of known bugs involving mob spawning; one of these (which is supposed to be fixed in the 1.14.1 snapshots) involves mob spawn attempts aborting if the pack spawning wanders across a chunk boundary. Given the dimensions of the farm, this is sure to be at least part of the problem…
If you've used a second account in spectator mode (or something similar) to confirm an actual absence of any hostile spawning (and the server hasn't lowered the mob cap or something similar to compensate for the poorer performance), bugs would be the most probable cause… [Unfortunately, this would mean waiting for MS/Mj to fix things… however, some reports have suggested that the effects my be location specific so one could try building at different coordinates and hope to avoid the issue[s?].
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WARNING: I have an extemely "grindy" playstyle; YMMV — if this doesn't seem fun to you, mine what you can from it & bin the rest.
Same/similar issue. I've built a grinder --- same design I've used a half dozen times on my playstation4. Now, on PC version my 4 level grinder only produces 1 - 2 spiders, or occasionally a couple of creepers and a skelly. My previous farms used to put out mobs pretty good. Now, it's either a few mobs, sometimes nothing. Anyone have any info on whether Mojang knows about this? And if so, is it some sort of designed-in feature, or is it a bug?