Hey folks, just wanted to follow up in case someone is having the same issue:
No matter how well I'd adjust it, it'll always come loose after a longer ride. So I pulled apart the adjustment screws, cleaned them up, applied some blue loctite on them and adjusted them until they felt firm but not too tight.
I've then taken the bike for a few rides and it stays firm. Sometimes it makes some noise while riding, which I imagine is the two ends of the fold rubbing each other. Probably unavoidable I guess...
Thanks everyone!