When I was playing as Mario against Sonic and Mega Man, when I went to summon an Assist Trophy, many of them appeared at once. For example, when Renji came out, another Renji would come out as well. When Protoman came out, another Protoman came out. Is this a common problem? Or is this something that happens alot? Can somebody answer those questions for me? Thank you!

This is not really that new, it already happenend before iirc.
Also I believe you should post this in the bugs thread.

I thought the bugs thread was locked. Thanks for letting me know about this.