With a balanced XLR output each channel has a + and - wire (4 in total).
SE connection has 3 wires total: Left +, Right +, Common ground (-).
Converting balanced XLR to SE by tying the two -'s together creates a short between the XLR -'s which is the “bad things happen to amps” part.
Some SE devices offer XLR connectors but they don’t have a true balanced (differential) electrical circuit. The SE common ground is wired to both XLR grounds. This is no-harm-no-foul since there was only a single common ground anyway.
It may be that some differential circuits survive having the channel grounds shorted, but do you really want to do that to your valuable equipment?