Let's just say I'm definitely the man to tell you about that train
There is only one camera for each carriage on each side. Most of the platforms are on the left hand side, therefore the cameras on the left are used. At New cross gate and Crystal Palace the platform is an "offside" platform, therefore the camera affected won't be used. Control would have had to make a snap decision during rush hour, so driver would've been asked to run fast to Crystal Palace, shut the train down completely to cold and dark, turn it back on and hope it's back. If it isn't then the affected camera still won't be used on the return journey until Dalston Junction, now the next "offside" platform.
"Degraded Dispatch" would've been carried out for a few stations prior, longer dwell time, slow speed leaving station etc. It's quite rare these days for camera issues on these trains, they're usually quite good now and even if there's an issue, comes back after two or three stops.