i’ve been doing long endurance rides for years now and they have almost always been fasted.
I have experienced everything you can think of, including what you described. Sometimes, it happens after 15, sometimes after 30 minutes, sometimes after an hour or two. But it goes away just as quickly as is appears without me doing anything special.
I believe it has nothing to do with nutrition, since I managed to ride for 2+ hours after this happened while eating/drinking nothing, except water. And even water was drank in moderate amounts, so it’s very likely not dehydration.
But maybe someone can provide a more scientific answer than me