I am also getting EXACT same issue with MAC OS 10.13.6 - BAD GATEWAY on all Sites. This has happened before (Nov 3) when I raised a ticket. Deleting this folder:-
Mac: ~/Library/Application Support/Local/lightning-services helped then but now makes no difference at all.
If I change PHP to a later version than 7.3.5 - Wordpress does not load - even after a 10 minutes wait. Go back to 7.3.5 & all is good.
Please help!