The biggest problem most of the lawsuits face is that there is a provision in the Terms of Service that basically says that Robinhood can prevent you from trading in any stock it wishes. Any complaint that amounts to "Robinhood violated its contract" is going to go down in flames as a result--it didn't violate its contract; the people who are complaining didn't read the contract.
That really only leaves two kinds of claims that might have legs: arguing that Robinhood violated securities laws, and arguing conspiracy on the part of hedge funds. The first part is difficult to win on because many of the complainants will simply lack the standing to do so (you have to have owned the stocks in question and bought/sold at a manipulated price to show standing, and since the complaints are generally on the theme of "we tried to buy but couldn't", they fail that) [1]. The last one might survive until discovery if properly pled, but I sincerely doubt they'll ever eventually win it.
[1] One of the cases filed for a temporary restraining order mainly on the basis of the complaint. The judge found that the briefing didn't even meet the "raises serious questions" burden of proof, although they mentioned that the TRO failed really hard at the "suffered irreparable harm" part because losing money is pretty much by definition a reparable harm.