Thanks for the detail opening thread. extremely helpful.
I would update your chinese made Huananzhi Motherboard to the latest BIOS version and your Powercolor RX450 I would check to see if it happens with a different Monitor without the HDMI adapter installed.
I would also check your RCA Monitor to see if there are any settings that might be wrong.
But, in my opinion, an adapter shouldn't cause any issues. All the adapter does it converts the VGA signal to a HDMI signal before reaching your RCA Monitor.