Just to follow up..
I received pin headers, on the C64C kit they go between 3.5mm jack and toggle switch – the board is very sturdy now and no issues with it flexing of moving when connecting the composite breakout cable. All good now.
Additionally, from my photos it was determined my VIC-II adapter was not inserted all the way. You shouldn’t be able to see the legs of the adapter – the board with VIC-II adapter should be flush with top of VIC-II socket. I had to press harder than I was initially comfortable doing, but eventually the adapter popped in and its flush with the socket – no more worries about it being loose.
Hojo_Norem was right about Yamaha RX-V867 receiver incompatibility. On my receiver I had to set “Analog to Analog Conversion” to OFF – and connect component output from receiver to component jacks on TV. With this setting ON, it will convert component input on receiver and output via HDMI on receiver to TV which is how I wanted it, but you end up with that scrolling. C64 Component kit also works plugged directly into TV or into OSSC, and looks excellent.
Thanks for the help, everything working as expected now!