Have you measured the DC voltage directly at the multis … Are you using back-up fuses on the multis … Are they ok?
Have you taken them out of the network and tested them individually?
There is a ceramic fuse inside …
@mrbart
How did you power up?
Just on battery, no ac loads or charging connected? A system should not be powered up with live AC in the beginning especially when they are not programmed.
Had you updated them firmware wise?
You would have to do the hard work now.
Remove it from the system. Check its internals are ok. No assembly issues. Test it as stand alone.