The target selectors ry= and rym= appear to be broken. I tested the following target selectors with both @p and @a in both a command block and in the chat bar.

[ry=-90]
Applies to targets with Horizontal Rotation greater than 0 or less than -89.0 (including all positive numbers)
This target selector is supposed to select only targets with a maximum Horizontal Rotation of -90

[ry=90]
Applies to targets with Horizontal Rotation between 0.1 to 90.9
This target selector is supposed to select only targets with a maximum Horizontal Rotation of 90

rym=90
Applies to targets with Horizontal Rotation greater than 90.0 or less than 0.1 (including all negative numbers)
This target selector is supposed to select only targets with a minimum Horizontal Rotation of 90

rym=-90
Applies to targets with Horizontal Rotation between 0 and -89.9
This target selector is supposed to select only targets with a minimum Horizontal Rotation of -90

Notes:
This bug is likely the cause of this person's problem MC-72378

When I used these target selectors in a chat bar while no one was facing a valid direction, the server would respond "The entity UUID provided is in an invalid format". Not sure if that's relevant.