Dual monitors on Pi5

Having some strange trouble getting dual monitors working with my
8GB Pi5. It only wants to use one of them.

Initially, the machine set up with an hdmi monitor on output 0
and an old DVI monitor on output 1. That did all I wanted, giving
sound via the hdmi output and extra screen space on the DVI monitor.

Overnight, the menu bar migrated to the extra monitor and I can't
move it back. The screen configuration utility doesn't recognize
the original monitor, though both monitors display at least some
boot output. At the moment, however, I get:
bob@raspberrypi:~$ xrandr
Screen 0: minimum 320 x 200, current 1920 x 1200, maximum 8192 x 8192
HDMI-1 disconnected primary (normal left inverted right x axis y axis)
HDMI-2 connected 1920x1200+0+0 (normal left inverted right x axis y axis) 519mm x 324mm
   1920x1200     59.95*+
   1600x1200     60.00 
   1680x1050     59.88 
   1280x1024     75.02    60.02 
   1152x864      75.00 
   1024x768      75.03    60.00 
   800x600       75.00    60.32 
   640x480       75.00    59.94 
   720x400       70.08 
HDMI 1 is recognized when it's alone and works properly, sound and all.
It's a standard 1920x1080 display.

Some months ago  a dual display worked fine with a DVI 1600x900 monitor.

I've tried both Wayland setups and X11, all behave the same at least in
regard to what monitors are active.

I believe it's important that the HDMI monitor be primary, in that it's
the only one that can provide audio output

At TNP's suggestion the power supply was replaced, raising the GPIO
rail to 5.45V, so I don't think that's the problem. I've also added
usb_max_current_enable=1 to config.txt, but that seems unlikely to
help the monitor recognition. I'll find out after sending this.

Thanks for reading,

bob prohaska