The log would normally be in your data directory. Are you sure you’re looking at the real log? (An internal server error will generate some sort of output within your log - unless it occurs upstream like at your web server or proxy, but that’s not the situation you’re describing).
Anyhow I would run occ config:list system to see what your parsed config looks like. Maybe a typo will turn up.
The log though is what you need to find.