I have exactly the same problem. On Sunday the control panel stopped receiving screenshots. Yesterday on the afternoon it received some for a couple of minutes and then it stopped again.
I don't know why lately Hoverwatch is having a lot of problems. It hasn't been sending also logs for Facebook Messenger nor WhatsApp voice messages. I have reported this several times with no convincing answer that really solves the problem.
Also when they release an update for the agent other features stop working that isn't solve until you update agent on target phone, which is not easy because we don't have access to target phone every time a new agent release is done.
Its really disappointing the support service and how the program works. They used to be good but since the last months only problems. Once I finish the subscription I bought I'll change to another software. It's a shame I bought 1 year subscription because I was happy with the service but right now I'm really disappointed.