I posted my log in the Minecraft forums and was informed this was an issue with Necronomicon, and that the version was not compatible with 1.20.1. I'm unsure as to why it would be an issue, so I posted here.
Here is the log: https://mclo.gs/i3HuN0L

This has nothing to do with Necronomicon, this is a packet issue and Necronomicon does not touch anything from mc's networking, nor has any packets.

Just because you see a warning on the top mentioning Necronomicon it does not mean that it's causing an issue, the warning you saw is from an old deprecated feature that wasn't yet removed.