any news on my crash bug that deleted my world?
I have been trying to duplicate it unsuccessfully. Bugs that can't be duplicated are generally called "gremlins" and I keep them notated in the hopes that if it occurs again I will have more information to help track it down and get it fixed.
A Concurrent Modification exception means that a mod is trying to read a list of data that is being modified as it is being read. It can mean 1 mod with a single line of code that is odd, or 2+ mods accessing and modifying the same information in the wrong order, or it can mean something is making the mods operate out of sync.
Imagine you are typing a paper on your computer. And you are sharing control with someone else and they start inserting sentences into the paper at different spots. Meanwhile a third person is trying to read the paper while the 2 of you are writing/editing it. That at a basic level is what is occurring when a Concurrent Modification Exception occurs. 70% of the time its a cross mod issue. The problem is it is very hard to track down what mods are interacting. You say you were placing a cover at that time, but thats not the only thing that was occuring in your world at that time. And duplicating the actions you described did not cause a co mod error in any test. Which means its something else that was occuring at the same time you were doing that, we just don't know what it was.
Frustrating as it is I can't get a fix if I can't narrow it down from 100 mods to at most 2-3 mods. Otherwise I am just going... "um mod devs there's a bug in one of the mods in DW20 pack... nope not a clue which mod or why but one of your mods has a bug"
I'm sorry. Large packs often have gremlins. Thats why if I can't duplicate it sometimes a bug report doesn't get a response. Because I am still tracking the situation in the hopes of figuring it out.