Can you put the power box at the camera?

Is a 16 port power box other cameras are also connected to it, apart 2 camera that I have issues with and both of them are in same building, so moving the power box to a particular camera is not possible.

It is if you fit a seperate psu on those cameras-temporarily even just to narrow the problem down.

As Rullland says fit a separate power box at the camera, I would imagine this will solve problem anyway, I think it probable that your camera is not getting enough power

Thanks all, I will try that