I've been playing the pack on my server for a while now, and it's been up perpetually for about a week or more. Recently we started getting some inexplicable serverside lag that appeared without a seeming cause, so to try and remedy it, I tried restarting the server. However, it became stuck, timing out due to tick simulation taking too long to process. I upped the maximum tick time from 60s to 600s, and it still timed out. I finally resorted to trying to open the world in singleplayer, and it's been sitting at 100% for the past hour with no changes.

Here's the world save; https://mega.nz/file/5At2HTrC#OYPEt6BNgl4tCnbsFbf58zMIsH3ROaTi6WSzSYGQ8Po

It's over a gig, so it'll probably a while to download. I've also attached the most recent server log file: latest.log
and here is the related crash report: crash-2021-11-29_18.48.08-server.txt

I doubt it's due to my computer, as I have a 9900k & 32 Gb of RAM. I suspect it might be related to the number of chunkloaders that we placed in the world to keep our machines running. I tried disabling them, but was unable to find the config options to do so.

Update: after some further fiddling, I was able to get the server to start again after opening up the world file in Amulet and deleting all of the placed chunkloaders that I could find. This did result in some minor world corruption, wherein some tile entities lost their state and had to be reconfigured, such as sequential gearshifts, rotation speed controllers and redstone links. Further, nearly all chiseled stone from chisels and bits was corrupted completely, becoming invisible, indestructible, gaining a full block hitbox, and causing immense lag while looked at. We had to remove all of the glitched chiseled stone using commands, which thankfully, was not a significant amount. I know there's performance overhead involved with using chunkloaders, but I didn't expect the world to just straight up stop loading!

Although our world is accessible again, I don't consider this resolved, as we never discovered the root cause behind why the chunk loaders prevented the world from loading, and we still are not able to use any chunk loaders for fear of encountering this glitch again.

Had a similar issue, just removing chicken chunks fixed my world from getting locked up like that.
I'm running the pack in a server and the day after increasing the range on the chunk loaders to its maximum I could no longer connect to the server, it would attempt to connect but would eventually time out and stop me from loading. I checked the server log and every time I would attempt to connect it would say "[Netty Epoll Server IO #2/WARN] [co.co.Connectivity/]: Login payload for Registry minecraft:item is using 27.1349% of max allowed vanilla size" and stop there. Attempting to load the world in singleplayer just resulted in being frozen at 100% while loading and not say anything useable in the logs. Removing chicken chunks from the client and server fixed the issue and recovered the world. Only had a flywheel in the nether that needed to be reconnected which fixed everything.

In the previous pack version the chunk loaders were stuck at 2 chunks so I placed a few around my base to keep major things loaded and I would be able to connect without any issue. After the recent pack update chunk loaders were now able to be increased in range so I increased the range of two of them, one in the center of the overworld and another in the nether with max range. I was able to keep playing with the chunk loaders at max range but was unable to connect after. The world kept running just fine though with all the chunks loaded.

Not sure if this will help, but this happened to me because of a blackout and the server didn't shutdown properly, I had to wait for a while for the minecraft server to respond when I issued commands (like whitelist list or any server commands), for 20 minutes, not sure if garbage collection was being ran by the server or what else was running to make it unresponsive for such a long time. Logging in will either give me a timed out response or I get in with the server suddenly being 600-800 ticks behind. I issued a /stop command and then restarted it, it took 5 minutes to be responsive again after starting. The world was accessible again with no lag whatsoever. Things that were running in the world was a bunch of create production lines, a few teleporters, a few ender tanks and chunk loaders.