If you have a spare computer/laptop, then you can watch the traffic on your connection between laptop and router (wireshark or any other tool that can listen to

If you have a spare computer/laptop, then you can watch the traffic on your connection between laptop and router (wireshark or any other tool that can listen to traffic in promiscuous mode). You can probably try it on your laptop as well though sophisticated malware/virus is theoretically able to "hide" it from you. Hopefully, traffic analysis can help you to identify the problem.