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Slime block piston elevator intermittently fails to launch players upward in Paper 26.3 #14344
Description
Expected behavior
When a piston pushes a slime block upward while a player is standing on it, the player should be launched upward consistently.
Observed/Actual behavior
On Paper 26.3, the slime block piston elevator works inconsistently.
Sometimes the player is launched upward normally, but sometimes the exact same elevator fails to launch the player.
No changes are made to the contraption between successful and failed attempts.
When the issue occurs:
The piston activates normally.
The slime block moves normally.
The player remains in contact with the moving slime block.
However, the expected upward launch velocity is not applied.
After several attempts, it may start working again, and later fail again.
This appears to be an intermittent physics/velocity issue rather than a completely broken slime block piston interaction.
Steps/models to reproduce
1.Create a simple vertical slime block piston elevator.
2.Place the player directly on top of the slime block.
3.Activate the piston so that the slime block is pushed upward.
4.Repeat the activation several times without changing the contraption or player position.
5.Observe that the player is sometimes launched upward normally, but other times the player is not launched even though the piston and slime block move normally.
The issue is intermittent and may require multiple attempts to reproduce.
Reference video showing the expected slime block piston elevator behavior:
https://packaged-media.redd.it/u3dpb8164ksh1/pb/m2-res_720p.mp4?m=DASHPlaylist.mpd&var=sgpssan&v=1&e=1791093600&s=826b92ca9a0ca43619dcd1fdbfbe2e19aac3c7cd
** This is not my video, but it demonstrates the same behavior.
Plugin and Datapack List
Paper Plugins (1):
- Timberella
Bukkit Plugins (4): - DiscordSRV
- LuckPerms
- WorldEdit
- WorldGuard
Paper version
[09:56:11 INFO]: This server is running Paper version 26.3-147-main@ddb45eb (2026-10-03T19:24:54Z) (Implementing API version 26.3.build.147-beta)
[09:56:11 INFO]: You are running the latest version
[09:56:11 INFO]: Previous version: 26.3-145-6bc56ab (MC: 26.3)
Other
This appears related to the previously reported issue:
#14327 - Slime block piston elevator no longer launches players upward in Paper 26.3
That issue has been closed, but the problem is still reproducible on the latest Paper 26.3 build.
The main difference is that on the current build, the behavior is intermittent: the same elevator can work correctly and then fail again without any changes.
Activity
Tom1817 commentedon Oct 4, 2026
hi, i can confirm that this is still a present issue on my server too, paper 26.3 build 143. We're testing with a basic sticky piston with slime block and a button in front. Interestingly, the piston will launch mobs and armor stands consistently without issue. The issue is also present on the latest build at time of writing which is 151
Tom1817 commentedon Oct 11, 2026
hi, have just updated to latest stable build and can confirm this is still an issue. To be clear, that is build 175
kennytv commentedon Oct 11, 2026
Can you try Vanilla, too?
Tom1817 commentedon Oct 12, 2026
hey, just tried on a fresh creative 26.3 world and it functions correctly. Just tested on paper build 177 and it's still broken
Tom1817 commentedon Oct 12, 2026
still an issue on 178 (pls tell me if you want me to stop confirming this each time)
Tom1817 commentedon Oct 13, 2026
still an issue on 181
Warriorrrr commentedon Oct 13, 2026
it's not necessary to keep confirming it, if you're subscribed to this issue you'll be notified automatically when it's fixed
Tom1817 commentedon Oct 23, 2026
Hi, I have just tested the latest build (218) and the setup is now very consistent (2 failures out of 30 consecutive tests). Something in build 215/216/217/218 seems to have resolved this pretty much completely
Thank you for your work on this, very much appreciated
pc1412 commentedon Oct 23, 2026
Unfortunately, the issue is still occurring rather than being resolved.
The slime block launcher continues to fail intermittently, regardless of whether I use a beacon with all available buffs or no beacon effects at all.
Based on my testing, the issue does not appear to be related to beacon effects.
Tom1817 commentedon Oct 23, 2026
Did you try it on a plugin-less server? i think you can just rename the "plugins" directory rather than having to remove them. It works fine for me with some fairly standard SMP plugins (essentials, multiverse, etc)
pc1412 commentedon Oct 23, 2026
I tested it under the same conditions, both with and without plugins, and the issue still occurred.
I don't have any plugins that should interfere with block or piston mechanics. Interestingly, the issue was actually worse when running the server without any plugins.
zvspany commentedon Nov 8, 2026
i can confirm that it's still a present issue, on 26.3 paper 244 build
kennytv commentedon Nov 8, 2026
https://mojira.dev/MC-312303