Can you specify the driver you are actually using, is the last driver for the FE?
Did you cleaned the drivers with a tool called DDU, before updating to new one?
Can you please specify the connector used to plug the two monitors on the gpu and the panels specs?
So to resume your issue, when you are playing on one monitor with the FE, you recall the Radeon Overlay with alt-R, enable the performance metrics.
At this point the metrics appear fine in game, but you second screen go dark/black with no signal or both go no signal?
Can you recover the screen signal loss in some way, i mean if you close the game or alt-tab, the screen come back working or the rig completely freeze?
I would advice you to try to clean the actual drivers with DDU, then reinstall the latest one downloaded from the AMD site.
I would try with other cables to connect the monitor, if possible, to check if it solve the issue.
I would try to check the monitors refresh rate and options, if it have something to do with the issue.