When I start the server (Linux, Ubuntu 18.04.5, 4GB RAM) everything is normal. But when I join, I can type, place/break blocks, but after 10-20 seconds, it kicks me for "Timed Out", and then in server list shows that 1 player is online - Me.
After 20-30 seconds, in console comes crash error, and after another 30-40 seconds, server shuts down.
I uploaded full log, from where server starts, to server crash end.
You properly set the gamerule randomTickSpeed to a very high value.
Please view (and maybe change) the value this gamerule in your level.dat file. I you don't know how to open and edit such NBT files, please ask at the Spigot forums.
As an alternative backup your worlds and try to reproduce with a fresh world.