Do you mean that in the model checker you explicitly marked the set as a symmetry set?
When checking liveness properties, you are not permitted to use symmetry sets. Per the "Symmetry" section of the built-in docs:
"Symmetry sets should not be used when checking liveness properties. Doing so can make TLC fail to find errors, or to report nonexistent errors."
At least in my build of TLA+, there's also a warning in the model checker when I have a temporal property being checked combined with a set being marked as a symmetry set.