When I do /reload on my server I crash. Unfortunately my hosts doesn't generate a crash-report when the server crashes so I cannot help with supplying a crash-report but maybe you could test it on a local machine? I know it is vault bc I removed it tried /reload and it worked then added it and did /reload and it crashed(Tested this multiple times).

Crash reports are required to debug issues like this. Just because the issue isn't present when vault is uninstalled does not immediately mean Vault is causing it. If you have other plugins that use Vault you should start there.