Suppression and Alistar
Alistar's ult cleanses it. It doesn't work on Sion during his ult either. Probably the same for Malphite.
So, uh, thought the point of suppression is that it is an unbreakable CC, no exceptions, unless you buy a QSS or MS.
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Alistar's ultimate is meant to clear ALL crowd control from him when he uses it, regardless of the type, but he will still be affected by crowd control effects used after he activates his ultimate. Gangplank's oranges work the same way, as does Olaf's ultimate (although Olaf will not be affected by any crowd control until his ultimate wears off).
When Sion uses his ultimate, he becomes unaffected by ALL sources of crowd control, no matter what kind it is. Same with Malphite's ult. Malphite is supposed to be immune to crowd control during the dash of his ultimate. Now, I say supposed to be because that's the intended interaction, but I haven't seen a Malphite in game for quite some time, so it might be bugged for all I know.
All of this is working as intended.