Sorry for bringing up this old post, but I've been struggling with the problem for almost a month now. I've tried many things - rewriting the start script, checking the logs for any error output etc. etc., nothing has helped so far. So I started thinking, that maybe the small amount of RAM is the reason for those unusual ''crashes''. So without doubt, I went for a 1024MB DigitalOcean VPS. And indeed, this improved the situation, however the NodeBB still crashes every now and then, but not on a daily basis anymore.
So I'm thinking that maybe there is a memory allocation problem with NodeBB or just NodeJS? I'm on NodeBB 0.4.3, not on the latest build ofc.
I'll do some tests and write back with some RAM allocation results.