You can host and play from the same computer without issues.
If two or more folks play suing the same IPs, it generally won’t crash the server. It often however glitches one or more of the characters that have connected.
Utilities that log and monitor various “things” while the module is up do not often help pin point the cause of crashes. Lag … yes. But even when something causes lag, it may or may not be the reason for crashing.
If the server “auto restarts” then most likely NWNX2 is in use and is capable of logging scripts and stuff already.
Does the server use the CEP? Players with a version other than the specific one used by the server can cause issues at times.
Anyone building in a module using CEP 2.4 or older when they have CEP 2.65 installed on their computer can corrupt areas/placeables/creatures unknowingly at times.
CEP 2.3/2.4 modules that didn’t later add the crash fix for Hardpoints Dragons can have unexplained crashes when a dragon using their appearance spawns in or appears on a clients screen. Not just crash the client, the whole server. Modules made with or updated to CEP 2.65 are fine.
Depending on what haks are used, sometimes their names overlap hak sets used elsewhere. I myself had some issues when other PWs used some or all of my own haks (which is fine, if I post it … go for it) and I had players hopping between my own and their PWs. Overtime, rather than add tophaks or other renamed haks as they expanded, they added things into the haks I had named and while it was fine “over there” it caused almost impossible issues, including some crashes on my PW. In the end, I ended up renaming my haks to resolve the conflicts.
Even the best profilers can fail to detect a script causing a sudden crash. Sometimes it all happens in an instant and the server processes have crapped out before whatever script is the issue gets logged.
Sometimes, most often when the server is used for other things like the Host playing, or just web browsing or the owner playing something else that can be the cause. Or a #@%!#^ windows update downloading.
Again … way too many unknowns. Rather than look for fixes yourself, because its highly unlikely you’ll find one, have the Host/Owner/Da Boss, come here and give details and ask for help. Some folk are just stubborn or are afraid of how they’ll look if they ask for help and some hosts have inherited a PW and host it but have no real experience maintaining, expanding or scripting a module. In these cases, they could still PM “someone” here in regards to their issues. The NWVault Discord Channel is another good place to seek assistance.