My group has been experiencing crashes with immersive portals, a mod that adds seamless transition between dimensions, I tried several minor fixes to things I thought to be culprits and even tried keeping both sides chunk loaded just in case, but after reading the logs of people affected, I saw that it was surprisingly giving them a crash due to "create" of all things. Specifically related to minecarts. I thought it was a fluke but sure enough over the week I have amassed 30 crash reports from my players all almost identical and starting with.

Description: Unexpected error

java.lang.NullPointerException: Unexpected error
	at com.simibubi.create.content.contraptions.components.structureMovement.train.capability.CapabilityMinecartController.tick(CapabilityMinecartController.java:105) ~[create:mc1.16.3_v0.3c] {re:classloading}

They are almost identical through the rest with only slight variations for numbers I don't want to bog the post down with every one of them though. I went onto the issue tracker to see if anyone had reported something like my problem and I found this.

#667

The person here also reports a crash log that is identical to the ones I've collected. But his makes more sense as he tried moving carts through a portal, but my players are simply walking through and the portal mods we are using are different. I believe he is also in 1.12 whereas my server is completely up to date.

Any insight would be appreciated I can provide additional log samples if you desire.

https://gist.github.com/1lop1234/2db84ff64d8c79936d1eb43acdaff071

This was addressed in 0.3e, feel free to re-open if its still an issue. Cheers~