Unable to join server

Whenever I try to join my server (it runs Magma 1.12.2 and I use Forge 1.12.2), I always get a message saying:

Internal Exception: io.netty.handler.codec.DecoderException:java.lang.IndexOutOfBoundsException:readerIndex(51) + length(2)exceeds writerIndex(51): PooledUnsafeDirectByteBuf(ridx: 51, widx: 51,cap: 51)

This has happened starting today, when I deleted a few mods and got TrapCraft. I tried deleting the world and that does not work. Haven't tried reinstalling server, gonna do that as last resort. Before I do that, can anyone help me? Or do I have to reinstall my server? I'm also using mods, just so you know, as well as a few plugins.

Plugins used are:

AdvancedBan

Captchas

ChestCleaner

Essentials

WorldEdit.

Too many mods here to list tbh.

Actually tried going from Magma to Forge again (as I had converted to Magma once) and I could get on now. Thanks for helping!

Btw, server ip is:

TheAwsomeMiner.aternos.me