How to reproduce:
1. Execute
/tp @s ~ ~ ~ 0 90 to put your viewpoint at the correct rotation.
2. Run
/say @s[y_rotation=0]and
/say @s[x_rotation=0]and observe that they both succeed, even though one of the values is set to 90.
One should appear as being false, as it is set to 90, not 0.
Thank you for your report!
However, this issue is a Duplicate of MC-121863.
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