This might not be related the your GPU setup at all. What RAM are you using?
I’m facing issues with my Framework 13 AMD laptop crashing too, the screen goes black and then reboots.
I’m using Team Elite 5200MHz RAM (2x 32GB), and apparently non-5600MHz RAM can be a source for instability when the system is connected to power. I don’t have the issue running on battery, which unfortunately you’re unable to test. Just letting you know as might not be due to your GPU enclosures, etc.