Yikes. That’s a LOT of money to be received ~weekly from an international source.
That means this has been going on for 2-4 months
This amount of money is likely to be reported to tax authorities if it hasn’t been already.
Is your son a talented artist of some kind? Musician? Video editor? Anything that might get them a contract job online that could be billed in different amounts each week? (A typical job would pay the same amount every week, whereas if they’re billing for “hours worked” it will be different each time)
I’m trying to be as generous as possible with explanations but I think you are right to be concerned (unless your son has a reason he would hide money from you, like a history of having his possessions disrespected or taken from him)
There are so many ways these trackers can break and they are almost always anonymised as aggregate metadata anyway by the tracking service
It is far more likely that they have been trying to call you or have expected some kind of response to the mail they are sending but have not received any contact from you in a long time