@Alex SImon Have you asked your PM?? How long did he/she take to inform you about the the two units not paying rent?
How did you find the PM, how's your relation with him/her?
When was the last time you spoke with the PM? Are you managing the PM? Getting regular communication from him/her and steering him/her? When was the last time you have been informed about the condition of the place? Have you inquired about it? Were the units checked recently? Any issues? Any repairs done lately? Etc etc. You have to know all this (and more!). If not, you're not properly managing your manager and he/she most likely became lazy and possibly didn't react to some complaints from the tenants and so on.
At this point I, personally, would not contact the tenants. Don't get involved, especially if there is and eviction coming up. But make your PM give you extensive information on what the heck is going on. That is what a PM is getting paid for: to be at your service.
And then, as has been said, inquire about the screening process and check if it's appropriate. But first understand what the problem(s) are.
Being a landlord is not about being lazy and just counting the money that comes in. It's a responsibility. And yes, you may have to go up there and sort things out... Good luck!