YES! My husband has this problem occasionally (much to his dismay!)
Started last fall; at first we thought it was due to the change in diet because we increased the fats since his weight was dropping. So we made adjustments. :-?
Then, he thought it was from take-out food or eating out; so, stayed home & I cooked every night.
I kept a journal of what he ate to see if we could figure it out, but there was no definite pattern.
And all the while, he wouldn't eat if we were going out (only to app'ts. etc.); definitely not good for the weight issues.
At his last clinic app't. we brought this up with his neuro. Neuro said that although ALS is not supposed to effect the bowels/bladder, he has seen it enough to think that is does. (although, as with everything else, not seen in all PALS)
He eats lots of fruit & veggies; we even tried the fiber supplements- they seemed to make it worse for him. Just feeling our way through this thing!