My sich hasn't gotten to this point yet but it will eventually. But it sounds like 1 of 3 things.
A.) She doesn't trust you with son alone. (A lot of women including my W lose trust in ex partner with kids, after they lose romantic feelings for partner, turn cold, some smother children more as their primary source of love, become more protective, etc. once seperated, and they will out-of-nowhere undermine our parental abilities as a "nurturing mother") I would take mine out of the house on my weekends to get him out, play in park, etc. She would call me to check in on me on how S1 was doing and how I was doing with S1 alone.
B.) She really misses her son. (Like what did you think was going to happen and what reality was going to be like seperated?) SHOCKER! RIGHT?
C.) She is using kids to temp check you. (Mine would send pictures during work day of "cutesy photos" of S1. Some things she invited me to which I declined, since I wasn't going to play family, she would send me pics of S1. Some she wouldn't. Some were at random. I would either reply one word answers or just stop responding all together. After all the radio/text/talk silence I couldn't tell if she was doing this to dangle a carrot in front of the horse? Or was just being/staging for being a polite co-parent?
You can ask the Vets here what to do, but I would politefully make it clear about non crucial communication, validate, and make it clear that S is fine, he's safe, well cared for, that it is YOUR PARENTAL TIME with S, and if you or her need anything, or need to communicate anything that is critical or informative, to do so, but only when necessary.
