Never heard about that association directly, BUT muscle relaxants are narcotics and as such slow digestion. A slower digestion may mean more
pressure on the LES due to (a) large meals,
and/or (b)
pressure on the abdomen (due to exertion, belly fat, or both), which would, over time, weaken it.
You may do well simply to follow a GERD diet (especially the part about "smaller, more frequent meals").