[oshirisuki]

I think sometimes not being able to get a software system with hundreds of thousands, or even millions of lines of code to compile is fine?

unless you didn't even do any changes, and it's a matter of the codebase requiring a specific environment or option to compile and you not having/knowing it

on getting better at debugging, I would try to isolate possible sources of the problem, form a hypothesis, test it experimentally

you'll need to know what you know

is it the environment you have? networking? OS? etc., whatever applies to your system

I think having a known working state is probably the most useful, though it might be difficult to get

something to consider, I do remember there being a paper on getting wrong results even when doing nothing wrong