Many thanks for the guidance and the warnings. And noted that the updates may/will over write whatever I have installed.
I have 2 Nexus 5 phones. One has hardware issues but works as my Guinea Pig device for trying something new in uncharted waters for me.
I moved your post to Devices/Google/Google Nexus 5
It seems your issue is related to this specific hardware and features so a better help may come here.
Sorry, I cannot help more as I never tried to cast video signal to another device.