After days and nights, weeks trying all Obs Camera, Ndi, CleanFeed etc (all paid versions) , I installed EPOC CAM PRO (Paid version.)
Finally a solution that works over USB/WIFI smoothly with Windows10 & IphoneX without any problem at all. Camera is always live, active as soon as I return to app after I receive a call or switch iphone windows, no loss of signal, no delay (Obs on ethernet cable, iphone on wifi at the same network), I did many live Youtube broadcasts / zoom etc /via Obs Virtula Camera) 3, 4 and sometimes 5 hours long, did not fail even for 1 second.
So I am quitting all the other progs for the sake of stability. One downside isonly one cam be active, dual or multi deviceas are not allowed. Anyway, I was never able to activate more than one iOs device before with previous programs I mentioned, so I am at least happy with a very smooth never failing single cam via iphone.