Thank you, I uploaded the video. The file was too large and I must have missed the error popup.
Still effects version 1.17
I'm pretty sure all the changes to ore spawns were reverted to 1.16 rules. The only one that's different is emerald ore. I assume emerald ore spawn rules are supposed to match 1.16 rules like the others, but it doesn't currently.
I used vanilla world generation, no datapacks. In the 1.17 world generation files, emeralds spawn between 6 and 24 times, I believe in 1.16 it was 3 to 8 times
I was able to recreate this in 24w18a in this test world:
[media]This world has two demonstrations. On the right, the zombies have their generic.movement_speed attributes set to 0.2 and 0.1. On the left, one zombie is given speed 5, while the other is unaffected. There are commands that log how long it takes for each zombie to reach the end. In both cases, the left zombie is twice as fast as the right zombie, but reaches the end nearly four times as fast.
In your test world, for some reason the speed effect was not applying to the zombies via the summon command, and both zombies were moving at the same speed. Using the effect command on a zombie after it is summoned works. That could be an unrelated bug.
When I first did a code review, I was on a 1.19 Fabric mod developer environment, which I believe uses Yarn mappings. That is what the code in the bug report is based on. I will try to look again for this code in 24w18a.