Hello again :D

I removed your mod for testing something with my modpack aaaaaand then I could not load my world anymore.
Something with datapacks are blocking my world.
(I know this type of bug, "Titanium" (the lib mod from Industrial Foregoing) had the same problem with disabling their gears in the config, but at some point they released a update to fix this - maybe you can ask them what they did, if you want to fix it very fast)

Ps: the "safe mode" button is hard useless -> it just don't work

Forge: 36.2.2
MC: 1.16.5
MMOP: 0.5
Meka: .448

Try bellow (This is a temporary solution)

1. Download NBT Explorer [Link]
2. Open level.dat in that world directory
3. Delete fml tag
4. Save and join world again

I found exact cause
it was related to register slurry to mekanism
it's my mistake

For solve this problem,
Dirty, Clean Slurries will register again as other name (internal registration name)

Thanks very much, for report this issue

607f03b
not tested yet

It seems to be a data tag related problem.
Can you upload the log file at the time?
or snippet of log when clicked 'safe mod'

I reproduced that problem

Hi,
I can test all the stuff and give you datas in ~6 hours.
(I need some sleep xd)
During the night, I had my gmx not open, sry.

Okay, here we go:

log with the loading fail: (0.5)

• 2021-08-13-1.log

World loading with first time -0.6:

• ohhhmmmmmm
  

I try the nbt explorer version and then I will update this post.

Log with 0.6:

• 2021-08-13-2.log

Log with 0.6 and deleting forge tags:

• 2021-08-13-1.log
  (world is loading)

Log without mod after loading with 0.6 and deleting tags:

• 2021-08-13-1.log

=
World is loading fine and problem is solved :D

Ty <3

That's good :)
Applaud your efforts 👏

take it slow
next version 1.16.5-0.6 was released
could you test that version later?