I hosted forge modded server using feather client
I was able to join without any issues yesterday, but today after I tested my shader on my single world then tried to join the world but it made error meassage. (I also changed server.properties's render settings, but I reverted it as same as yesterday)
So I removed my shader and removed optifine on server and on my mod file then it made this error:
Internal Exception: io.netty.handler.codec.DecoderException: net.minecraft.ResourceLocationException: Non [a-z0-9/-1 character in path of location: inecraft:ask_server\u0012\u0001\uFFFD\n\u0007targets\u001D\u0001\u0014minecraft:ask_server\u0012\u0002\uFFFD\n\uFFFD\n\u0002id!\u0014minecraft:ask_server\u0002 \u0001\uFFFD\n\u0006target\u0006\u0001\u0002\u0001\uFFFD\n\ttarget



My server/client is 1.20.1 forge.
And I got 34 mods total, it was working pretty fine yesterday
(I did not add/remove any mods before it started happening)

I hope it's not about my worlds, it's been quite long since using this world

I'm not native english speaker so there may be grammar issue!

Thank you for reading!

I just backed up my world then tried to create new mod with currently equipped mod but with new world still made same error.
Sooo I think it's not world error. also It's working fine on singleplayer.

+ but it made some another weird error with new world

Edited January 24Jan 24 by Rikoring

After reinstalling and rebuilding server, now I get another error which is
Internal Exception: io.netty.handler.codec.DecoderException: java.lang.IndexOutOfBoundsException: readerIndex(2829) + length(1) exceeds writerIndex(2829): UnpooledHeapByteBuf(ridx: 2829, widx: 2829, cap: 2829/2829)

Please read the FAQ (https://forums.minecraftforge.net/topic/125488-rules-and-frequently-asked-questions-faq/) and post logs as described there.