Internalisers do not "front run" retail orders. That's not even a thing you can do; the idea of front running is to get ahead of a trade that will move the market, but the internalisers are buying retail order flow because it won't. If the order isn't moving the market, you can't "get in front of it".

If front running happens at all (and by strict definitions, it really doesn't), it certainly isn't happening to Robinhood customers (or the custoemrs of any other discount brokerage).