I found a bug in my playthrough, and was able to track it down to this mod. not sure if it's been reported yet or not (I couldn't find it when I searched) but moon lord spawning makes all blocks (except water, honey, and items dropped, that I can tell), completely disappear, making arenas just about worthless. I have to turn this mod off to fight him, because otherwise I'm running into blocks that are supposed to protect me from the deathray, and sometimes I'm not under them at all, I'm under platforms instead, which of course gets me hit. It's all just a black screen with the water & honey. I do use several mods, but I went through, enabling them one at a time & spawning him in, until this mod alone was enabled & the blocks still disappeared.
First 2 screen shots just show my arena set up, what it should look like. 3rd screen shot, obviously, shows everything that's disappeared, even the druid that was standing there. The last screen shot shows that my heart generators disappeared, but the items that the statue spawns have dropped still show.
This bug has now happened to me a BUNCH of times, over the course of a month or so. It just took me this long to get the motivation to figure out what's going on. It's happened in 2 different runthroughs, with different mods being used too. But it also happens, as I said earlier, when only this mod is enabled.
Last (hopefully helpful) thing I can think of is I've also tried it with different blocks. When this happened the first time, I immediately modified my arena to use the basic wood blocks instead of gemspark, and it still happened.