Open adoption? Never again.

My son is about 7 months old. His birthmom has had no contact since the placement, although we have an open adoption. I have been sending her the letters we agreed to and asking if she wants to do the visits we agreed to every time they roll around (there are supposed to be 4 a year), and leaving the ball in her court for when she is ready. She responded to my last inquiry about a visit and we agreed to a place and time. At the agreed upon time, she texted that she was running 30 min late, then she texted 30 minutes later that she was just 20 more min late, then it was 15 min, then 5 min, then another 20 min, and so on until it had been 3 hours and 45 minutes. At that point, it was getting close to his bedtime and I texted her that we had to leave (he was fine chilling for those 3 hours and 45 min, we were somewhere he likes, he's a baby so if he's getting his bottles and someone he likes is with him he's pretty much good). 15 min after that she texted "Where are you I'm here?!" I then got a butt dial from her and could hear her asking people if they had seen us and explaining she was supposed to meet her son's adoptive parents. I texted "We had to leave, I'm sorry we missed you. Hope we can see you text time."I'm not sure where to go from here, especially because she's given me no explanation of what happened during the nearly 4 hour delay. I don't know if she was too anxious or sad about the visit, if she simply had transportation problems, if she got high (she's active in her addiction to heroin), or if there's another explanation.Just schedule another visit the next time it's due? Reschedule this one? Change something about how we schedule it? Demand an explanation or leave it be?I'd appreciate your thoughts.