Describe the bug
Another issue with Sync, but I got one shot by something, and becoming salty on the server, I proceeded to use the grace time to dig myself a minor clone lab with other bits and pieces. A few things arose from this chain of events.

Building clones while dieing gives the clones the health you had when you activated the builder.
Switching from from dieing body into a not dieing body suspends the regeneration, but I think cause it was created mid grace it had the desaturated screen and greatly reduced health, but it seemed fine to move around in.
However, switching back to the dieing body (due to I forgot to get my item into a crate) crashed the server with the attached crash lags and kicked everyone out. When I relogged, potentially as a side effect on sync combined with the perfectly timed crash, all my stuff was deleted. :<

but it was an interesting interaction, albeit saltened by the loss of equipment.

Later, after a switch back and forth creating two more crashes, I was capable of just watching the sunset as I went critical in a cinematic fashion as the world went dark and I popped like a cherry tomato and went into a shell. unfortunately it was a mid death clone, like all the others cause it was all done during a single regen grace phase, so i had no pure clones prior without the negatives carried over from the state. and so had to regen to fix them.

To Reproduce
Steps to reproduce the behavior:

1. get sync set up.
2. die and enter grace.
3. make clone. then switch to it.
4. witness reduced stats and always desaturated vision carry over... Then switch back to dieing body, and witness crash and item deletion due to double whammy bug implosion.

Expected behavior
This was probably quite understandable that it would happen, but item deletion was salty but probably on sync's side and so it couldn't finish producing my items. But figured I'd report and see if you could fiddle with this rather novel combo of death evasion.

Additional context
was on the server, but will probably have a similar effect on a small pack with just the two available in singleplayer.

It seems you have forgotten to attach the log files you have mentioned in your initial post, could you attach those for further investigation please?

sorry, got distracted by my game loading up finally. I was gonna test a version of this in single player for a proper crash. which is here now:
https://paste.dimdev.org/joqevugabe.mccrash

crash-2020-02-21_07.45.17-server.txt
crash-2020-02-21_07.51.37-server.txt
crash-2020-02-21_07.55.08-server.txt

edit: re-upped cause something screwed one of their links. but they should all be the same anyway. same problem

Ahh, I think I see what's happened here
The setup of our system, written initially by @HoldYourWaffle, doesn't support just stopping a Regeneration Stage

For example, in this instance you were in the stage "ENTER_CRITICAL" and Sync has moved you to another instance of you(?) and my mods capability has just become confused, I should be able to fix this hopefully, but it may take a little bit of time

I'm actually really glad you're reporting issues from Sync, as someone I know uses it and wanted to use it with Regeneration in the near future for a server haha

well damn. glad to help I guess. good thing I got projectE on server. i'll be back up to speed in no time. working on a nice village refurbish for fun with MCA villagers. so, will just backrupt the economy (if it wasn't infinite) a little and shower everyone in nice things for their highly EMC dense emeralds and will be fine, after the salt goes away.
But glad they're fixable.

Anyway, yeah, sync is pretty much a glorified death prevention and teleportation with a drawback mod. since each clone is it's own instance with buffs and health stats etc. Like, I remember back in the day it'd keep your thaumcraft research and other forms of mod based skill/custom progression and stuff when you'd switch. which was particularly fiddly and all sorts of annoying to work around. (make any progress and you'd have to update all your clones or risk losing some on death).

old body would still drop your stuff and react like a death, but the full death would get negated and you'd turn up on the clone instead and have to go get your stuff. and each clone has it's own inventory, so it'd store inventory contents, so you could fit all the clones with gear before hand incase of emergency. and I think the custom progressions and research systems got good enough/sync got smart enough to not record that stuff. Although it still takes baubles and external accessories with you no matter where you go. which is funny. so atleast I kept my aether accessories and baubles.