The problem may actually be that, since 1.8 is out, tick lags make the beam disappear and the effect often disappear and reappear, and it make the inventory UI move lots of times...
If you have time to open a new ticket, short and complete, saying that we are several players saying on Jira that these news kind of lag are a real problem in multiplayer, it would be perfect.
Maybe quote some things we said, so that the moderator can understand it's not only you, and it's on world that made the direct 1.7.10 to 1.8 upgrade without using snapshots :/.
So the bug is : Tick take sooooo much more time than ever 😞.
Ok...
So the bug is : I never had lag before 1.8, now I have a looooot of it. Especially Tick Lag that makes Horses, Minecarts, Beacons, Boats.... Useless...
And people say we can't go back to 1.7.10 without losses 😞.
New dungeon was supposed to spawn in 1.7-generated chunks, they are not on my server :/.
But the Guardian mobs are spawning (not the elder one).
And I never ever had so much "[Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 3739ms behind, skipping 74 tick(s)" before oO
Same problem on a server that never used any snapshot or mod...
Minecarts, Redstones, Mobs, Horses .... Everything is like ten times slower for everyone on the server 😞.
We walk faster than minecarts and horses.
Actually, the problem is the same if the block under the Slime isn't a piston.
Same here, our world existed loooots of versions ago.
In 1.13 we were able to play with 4-5 players (maybe more) with a rendering distance of 12.
Now we downgraded in 1.14 to a 8 chunks distances and it's still very slow, and the server crashes often 😞.