Wow! Someone with more cameras than me! lol
A couple of things that I can think of:
1 ) Make sure you have adequate connection strength. Just because it is "connected" doesn't mean it is adequate. I was having the same issues, and I finally replaced my wireless router, and it made all the difference in the world. Your router has to have enough hardware to handle more devices and priority since technology is expanding in leaps and bounds. Unfortunately, people tend to buy and add many newer devices and the router is the last to be replaced and never considered. I bought a ASUS RT-AX86U, and it has a 4 core cpu and plenty of RAM, and is designed for large homes. (not trying to sell anything), but it was the best thing I did. It solved all my problems.
2) Make sure your internet plan has enough upload bandwidth. I have 6 Nest Cam (floodlight), and a Nest Hello doorbell, Nest Thermostat, 35 lights, plugs, etc. etc. and you have to realize that suddenly, all your devices, including cameras have to "serve" from your home. Your home/router needs to have the ability to serve/stream to the internet. I'm sure your download speed/bandwidth mps is fine, but what about the bandwidth for your upload speed? Once I added the 7th camera, I was maxing out my upload bandwidth and it did get a little sluggish viewing all 7 cameras at once, outside the home.
These are just a few things to consider. The router made the biggest difference and solved other device connections, not just the video. I like that it has only one SSID and maintains the dual band on the backend. (2.4 and 5GHz), it is also WiFi 6. The cameras are dual band as well and will connect automatically to either band. I have all my cameras set on Max video, so serving (streaming) from my home is pretty hefty when I'm viewing everything.
Good luck.
