Try increasing the size of your swapfile. Mine was 2GB (default for Ubuntu) and after I increased it to 8GB the crashes stopped.
For your setup I'd set it to 16GB.
You have old A18 mods in use, for example Stallionsdens Stack Size Increaser. He recommends using Claymore's stack size
increaser instead. And your Wireless Power Box mod is very likely not compatible with A19.
Try reducing your MaxAllowedViewDistance from 12 to 8 or so. I doubt anyone will notice and it reduces memory and cpu use
on the server.
Reduce your MaxSpawnedAnimals and MaxSpawnedZombies. There's reports of bugging out when using numbers higher
than the defaults. (50 and 64).