Good troubleshooting wholesomejoe. I know the headache of this, one time I purchased a brand-new breadboard and re-done many circuits on it, turns out the breadboard never had good connections from the start.
I am not sure if it was the manufacturing oils used on the busbars or a plating issue. I went back to ole-trustworthy for the time being but I suppose I could have gave it a shot of contact cleaner. Either way you’re not alone in these breadboard frustrations.