Thank you for the reply Alcoholocaust and for the clarifying information.
Thankfully the warnings and errors are pretty straight forward.
If you go to your WorldSettings level and click build > LightingOnly, does that same error show up after the lighting is built?
If your lighting build fails, Dongas has a pretty nifty step-by-step solution, though it is for a much older engine version if you’d like to try.
For the warnings, I would try to remove those assets and place them back into your level or check the collision type.
I hope this and the other link I sent you earlier helps you resolve this.