After crashing the server 3 times in a row around a week ago and looking at the crash report that came from the crash I came to the conclusion that loading a certain item, that is found only on the End City chest loot table will cause the server to instantly crash. The item in question seems to come from the Floralchemy mod, which is a small Botania addon that adds 7 items. One of these items can spawn in a chest that is only found in End Cities. Loading the chunk where this item has spawned will cause the server to immediately crash.
I've explored over 15k blocks in the End and have crashed the server 5 times even though I've found far more than 5 Cities. Loading an End City that does not have a single chest will not crash the server, but there isn't a 100% chance that the item will spawn even when there is a chest somewhere in the City. Something that is consistant with the End Cities is that they will often have parts, or even entire towers missing. The first End City I found had a tower that was cut entirely in half. Another consistant behavior of the End Cities is that they have been completely wiped of all loot. Luckily this isn't a big problem since the only treasure is stored on an item frame, that being the elytra. These towers are not destroyed at their chunk borders though and I cant find any other patten to it.
The worst thing about this is that there are possibly 100's of End Cities with this item just lurking to be found. I'm not sure how big the border is, other than atleast 16000 blocks out.
On another note, if the border in the End is made to dictate the amount of Chaos Guardians in circulation, then more and more End Cities will be out there. Also while on the topic of borders and Chaos Guardians, if the border is at any lower than 20500, then it is impossible to create the ATM Star, thus blocking off the absolute best armour in the pack.
I'm not entiery sure, but this crash might be related to the block dissapearings that have happened the past few days. After the server restarted today due to me finding one of these cities, a players base was missing random blocks, pieces of a smeltery to be precise. Luckily I could not find any damage in my base after the server had restarted.
