Seems like any recovery move that doesn't leave the character helpless can be used twice in a row if you jump and use it at the same time (with the exception of Sora for some reason, he just gets some fancy gyroscope trails while standing in place)
Sonic can UpB twice too, but you need to use an attack first before UpB'ing again
Note that he still loses his air jump, and the spring jump only goes slightly further up than a normal double jump, so this isn't anything crazy at all, more like if you want to show off
Also, yes you do get a bugged helpless state, but it won't "softlock" your controls and you can still drift around, this will only happen if you try to UpB again before attacking first as i've found out
quick edit:
It seems that with this tech however, Sonic can use his NeutralB/SideB right away after a spring jump, instead of only his DownB