How Can I Systematically Investigate Repeated Security Camera Failures and Strange Wi‑Fi Behavior?

Since moving into our home, we've had problems with several different security systems. Google Nest cameras lost access or recording history, an ADT system appeared to disable itself, and a wired Night Owl PoE setup had missing recordings, cameras going offline, unexpected lights turning on and off, and occasional loss of access. The equipment was eventually exchanged, but similar concerns continued. We now use Vivint, and its account history shows that an unfamiliar profile was created and the PIN was changed, even though we did not make those changes.

We've also noticed that only a couple of Wi‑Fi networks appear when we scan from inside the house, while many more become visible outside. Friends have observed the same thing. I'm not assuming anyone is deliberately interfering with our network; I'm trying to understand whether this could result from building materials, signal propagation, router settings, interference, power problems, defective equipment, or unauthorized account access.

What would be the most objective way to troubleshoot this? Should we replace the router and networking hardware, isolate the cameras on a separate VLAN, collect router/NVR and authentication logs, test for RF interference, or hire a professional to assess the network, wiring, and electrical power? We want reliable evidence rather than speculation.