That's a crash. Not a rendering issue, i think.

this crash doesn't occurs everytime, it's a little bit random. It happened to me while using the dimension changer item from aroma's mining dimension mod but not at every try (sometimes it works and sometimes it crashes)

I also use the betterportals mod that enchance third-party transferts.

crash report : https://pastebin.com/pHB7QcSW

since I'm not sure that it is your problem, i have reported this crash on the betterportals issue tracker too. Johni0702/BetterPortals#403

Looking over the code, literally the only way this can occur is if there's a race condition, which would explain why it's intermittent. When I have more time I'll see if I can reproduce this and create a fix.

@thecodewarrior
The WorldEvent.Load is fired on the client and on the server and if the server happens to be an integrated one, then there's your race condition.
gettingWorld should probably be a ThreadLocal instead.