Joined friend's server, have been trying to get optifine to work with MCMT and finally got it to work by using the fabric mod ports of those. At first everything was fantastic, but after a bit (specifically the first time i tried opening a custom menu with a magic plugin we have, which uses custom icons) it disconnected me from the server automatically. Ever since then, it disconnects me whenever I click and pick up ANY item with my mouse (it didn't do this before).

Further info that may help: Server has a bunch of plugins that add custom textures, and the server has a custom resource pack to go with it. The other mods I have installed (fabric) are MCMT fabric, xaero's minimap fairplay edition, farsight mod, Light overlay, Manningham hills (idk where this came from, probably an automatically generated mod dependency), Mod Menu, Roughly Enough Items, Cloth API, Architectury API.

The following is the output log, showing warns and errors.

17:53:01.746
Unused frames in sprite minecraft:missingno: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
17:53:01.755
Unused frames in sprite minecraft:missingno: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
17:53:01.767
Unused frames in sprite minecraft:missingno: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
17:53:01.780
Unused frames in sprite minecraft:missingno: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
17:53:02.410
[OptiFine] Unknown resource pack type: net.fabricmc.fabric.impl.resource.loader.FabricModResourcePack@4fc139cf
17:53:02.413
[OptiFine] Unknown resource pack type: net.fabricmc.fabric.impl.resource.loader.FabricModResourcePack@297508ff
17:53:02.414
[OptiFine] Unknown resource pack type: net.fabricmc.fabric.impl.resource.loader.FabricModResourcePack@638ab0a7
17:53:02.770
[OptiFine] Unknown resource pack type: net.fabricmc.fabric.impl.resource.loader.FabricModResourcePack@f459c2f
17:53:02.964
[OptiFine] Unknown resource pack type: net.fabricmc.fabric.impl.resource.loader.FabricModResourcePack@6f67495e
17:53:02.965
[OptiFine] Unknown resource pack type: net.fabricmc.fabric.impl.resource.loader.FabricModResourcePack@d1ce0b9
17:53:13.893
Error receiving packet 8
java.lang.IllegalAccessError: class it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap$MapEntrySet tried to access protected field it.unimi.dsi.fastutil.ints.AbstractInt2ObjectMap$BasicEntry.key (it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap$MapEntrySet is in unnamed module of loader net.fabricmc.loader.impl.launch.knot.KnotClassLoader @604c5de8; it.unimi.dsi.fastutil.ints.AbstractInt2ObjectMap$BasicEntry is in unnamed module of loader 'app')
at it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap$MapEntrySet.fastForEach(Int2ObjectOpenHashMap.java:1075)
at it.unimi.dsi.fastutil.ints.Int2ObjectMap.forEach(Int2ObjectMap.java:255)
at it.unimi.dsi.fastutil.ints.Int2ObjectMaps$UnmodifiableMap.forEach(Int2ObjectMaps.java:691)
at net.minecraft.class_2540.method_34063(class_2540.java:170)
at net.minecraft.class_2813.method_11052(class_2813.java:52)
at net.minecraft.class_2545.method_10838(class_2545.java:45)
at net.minecraft.class_2545.encode(class_2545.java:14)
at io.netty.handler.codec.MessageToByteEncoder.write(MessageToByteEncoder.java:107)
at io.netty.channel.AbstractChannelHandlerContext.invokeWrite0(AbstractChannelHandlerContext.java:717)
at io.netty.channel.AbstractChannelHandlerContext.invokeWriteAndFlush(AbstractChannelHandlerContext.java:764)
at io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:790)
at io.netty.channel.AbstractChannelHandlerContext.writeAndFlush(AbstractChannelHandlerContext.java:758)
at io.netty.channel.AbstractChannelHandlerContext.writeAndFlush(AbstractChannelHandlerContext.java:808)
at io.netty.channel.DefaultChannelPipeline.writeAndFlush(DefaultChannelPipeline.java:1025)
at io.netty.channel.AbstractChannel.writeAndFlush(AbstractChannel.java:306)
at net.minecraft.class_2535.method_36942(class_2535.java:214)
at net.minecraft.class_2535.method_10761(class_2535.java:206)
at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:164)
at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:469)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:500)
at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:986)
at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
at java.base/java.lang.Thread.run(Thread.java:833)
17:53:14.322
[OptiFine] Unknown resource pack type: net.fabricmc.fabric.impl.resource.loader.FabricModResourcePack@1a1c34cf
17:53:14.322
[OptiFine] Unknown resource pack type: net.fabricmc.fabric.impl.resource.loader.FabricModResourcePack@1a1c34cf
17:53:14.322
[OptiFine] Unknown resource pack type: net.fabricmc.fabric.impl.resource.loader.FabricModResourcePack@1a1c34cf
17:53:14.322
[OptiFine] Unknown resource pack type: net.fabricmc.fabric.impl.resource.loader.FabricModResourcePack@1a1c34cf
17:53:14.444
[OptiFine] Unknown resource pack type: net.fabricmc.fabric.impl.resource.loader.FabricModResourcePack@52f0600e
17:53:15.478
Unused frames in sprite minecraft:missingno: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
17:53:15.498
Unused frames in sprite minecraft:missingno: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
17:53:15.517
Unused frames in sprite minecraft:missingno: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
17:53:15.523
Unused frames in sprite minecraft:missingno: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
17:53:15.531
Unused frames in sprite minecraft:missingno: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
17:53:15.539
Unused frames in sprite minecraft:missingno: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
17:53:15.929
[OptiFine] Unknown resource pack type: net.fabricmc.fabric.impl.resource.loader.FabricModResourcePack@64a21865