I'm glad to hear that it works again, but do realize that our stated minimum spec for good detection quality is 5 fps. At 3 fps you may occasionally still be missing something.
Regarding the number of cameras -- Yes, 18 cameras is a lot, but it probably works because your resolutions and frame rates are both low. I'm not actually aware of anyone else running that many cameras.
Our rule of thumb is up to 24MP of total camera resolution for normal home security usage, but we rarely find people using resolutions lower than 1080p, so we don't have a lot of data for more than 12 cameras at a time.
However, with that rule of thumb, we're assuming about 25 fps per camera, so having the frame rate lower than that cuts down processing a lot, and I believe you're actually also under the resolution limit.
If you're getting close to the processing capacity, you'll see messages saying "Camect Home is Busy" on some camera views, and if you're steadily overloaded, you'll get messages below the display of cameras telling you that the device is overloaded an suggesting that you disable some cameras. If you're seeing neither of these, the number of cameras is probably fine.