Ubuntu 16 LTS, i7 CPU, 64 GB RAM, 480GB SSD storage

Thanks, that seems pretty useful... if I improve my starship plugin's relighting and clean the light of every world with that plugin maybe I can enable random light updates

This plugin might be useful for you:
https://www.spigotmc.org/resources/light-cleaner.42469/

Oh and I know my world got like this because of my starships plugin, that's why I want random lighting on in the first place! But random lighting makes it try fixing on chunk load in addition to the actual random lighting and that seems to make it not work well, so I just want it to only do it randomly.

Is there a way to make it so it does random light updates but it doesn't relight them when they load?

There is no bug here.

You have a tonne of unlight chunks with complicated light filled structures.

Enabling random light updates will cause their lighting to be recomputed which is slow and where you see lag.

Disabling the random light option, there is no lag and the option is working correctly.

It means its not a priority and because we don't know how your world got like this (and no one else has had this issue - it could be caused by a plugin) we may not be able to provide much more advice than "delete the affected chunks"

Does that mean I cannot get spigot support on this?

Oh wow, I was not aware of this.

>Vanilla Minecraft has no random lighting,

Yes it does, it's always enabled and has been for years (possibly forever).

http://prntscr.com/hmapmm console log from uber lag time

Not sure but it seems to freeze a lot when loading chunks with broken lighting like this: http://prntscr.com/hmaoze

http://prntscr.com/hmanys screenshot with coords of a place that has infinite death

Vanilla Minecraft has no random lighting, but I tried it anyway. The weirdest thing happen - not a single chunk would load??? It instantly timed out! I rejoined and experienced the same ridiculous lag I get from random light updates. Perhaps enabling random light updates indirectly actives infinite lag that was also automatically activated in 1.12.2 or something!!??!?!? As for the world file.. https://1drv.ms/u/s!AlDbRpW3H6lAv_kBAp_22RWhsjnufQ It wouldn't let me attach it, so I just uploaded it to onedrive.

If you have a section of a map that reliably reproduces this issue then you should attach it to this ticket.

You should also check using the vanilla server

I dunno about the 1.12.2 thing, however I'm 100% sure and can repeat every time the server lagging to death when I use random lighting even with 0 plugins. I can send the world with the issues if you want, it's 1.6 GB

I have not seen this anywhere else, and random light updates did not change on 1.12.2 (nor do any of your error messages show anything to do with random light updates).

If you have a section of a map that reliably reproduces this issue then you should attach it to this ticket.

You should also check using the vanilla server

Yep, definitely still freezes with random lighting. Original issue is still a thing, but maybe the secondary issue where it's forced on is gone. Still need help fixing random lighting!

Crash report with random lighting enabled, no plugins but multiverse and essentials, occurred right after it froze when I joined. crash-2017-12-10_12.15.55-server.txt

No such luck, still freezes with it, too bad...

Seems like the option for random-light-updates is a thing again as well?? Maybe the time I tested it before I had an older version of spigot and the random lighting updates not being optional was fixed. I'm going to try it with random lighting updates again and see if those magically work now.

We didn't use viaversion back then. Perhaps viaversion fixed it! xD

Timed out issues are likely caused by changes to the keep alive packets by Mojang. Spigot increased the timeout value from 15 seconds to about 30 seconds. Since you're running ViaVersion this won't work well with clients running older version. So you should use a BungeeCord server as a proxy that will handle the keep alive packets. And you could run ViaVersion as a BungeeCord plugin which will also cause less lag on your Spigot server.

If you need help setting up a BungeeCord server please use the Spigot forums.

I still had the main issue without any plugins at all, not even multiverse. I will see if the crash can be reproduced without any plugins though. EDIT: Except multiverse and essentials, for convenience mostly

Crash logs shows no indication of lighting. The crash is likely caused by one plugin.
So please try to reproduce without the plugins Erudition, Starships, ExplosionRegen and FastAsyncWorldEdit.

UPDATE: I tried it again, and it seemed to load chunks just 'swell. I thought that a miracle occurred and it fixed itself - until while flying around at speed 10, the server suddenly and inexplicably crashed.crash-2017-12-10_03.42.03-server.txt