I initially thought sponge was the problem as that's when the problem began, but after posting on sponge forums I have been pointed in this direction. here is the log from a crash. I am playing tekxit 3.14 on my server and the minecraft version is 1.12.2 if that helps.
https://github.com/crush2021-1/latest-log/blob/7efe42d6b77e1b08390ce35027f581de1232e3a1/latest%20log%20820
mixins.bugfixes.world.chunksaving is what brought me here
I have already changed the config for sponge but it hasn't solved the problem. Let me know if you need anymore info or another log, thanks.

Looks like features from Universal Tweaks are incompatible with SpongeForge. Please disable Entity Tracker under Bugfixes -> Entities and Chunk Saving under Bugfixes -> World inside the Universal Tweaks config and try again!

Sorry been away. Just applied the changes, but the server still crashed after entering the nether.

I should also note that I did try uninstalling Universal tweaks and that didnt solve the problem either.

Are you able to test without using SpongeForge? Just to rule it out.

Ya without sponge forge it works perfectly fine, however I already posted on it regarding sponge but they pointed me here.
Here’s the link to the forum if you want see what we already covered.
https://forums.spongepowered.org/t/just-added-sponge-to-my-tekxit-pi-server-and-it-crashes-every-time-we-go-to-the-nether/42011

Is there any reason you‘re using a heavily outdated version of SpongeForge? I threw the latest version into Tekxit and could launch and switch dimensions just fine.

I thought i was using the current version Ill try it

still crashes in nether

Odd, won‘t for me.
Do you get an actual crash report? If so, please share it.

https://github.com/crush2021-1/latest-log/blob/53738729aca9977ce97d30621ad8bf532939a132/crash%20report%20625
theres a link to the latest crash report, there are also some logs if you would like to see those aswell

Sponge itself is failing at processing advancements, possibly the ‚We Need to Go Deeper‘ advancement upon entering the Nether. Nothing we can do from the MixinBooter/Universal Tweaks side.