The server has worked perfectly for months. Then, at some point, I updated Paper (from 347 to 380) and after a restart:
#1 https://pastebin.com/3jWkvkM0
#2 https://pastebin.com/D8RUSZcb
#3 https://pastebin.com/qQz0sA17
#4 https://pastebin.com/SWqMj7Lg

Then I disabled the async chunk load in paper.yml and the server held up for half an hour.
Afterwards, it lagged (as before) and a few seconds later it crashed:
#5 https://pastebin.com/ntGCytGH

I restarted it and after a few seconds:
#6 https://pastebin.com/kfaBVdas
#7 https://pastebin.com/EXWXsFFm

I tried to use Paper #379 and Paper #380 but nothing. I use Aikar's flags with 6GB of RAM. My KVM specs: https://pastebin.com/sL6S7smA