Can't find my Opponent in Multiplayer 1v1

[Grendel88]

My brother and I have played over 10 1v1 scenarios in Multiplayer OOB, but since this week we can't find each other's challenges in the Open Challenge window. Whether I or he post a password protected challenge, we can't see each other's challenge in the multiplayer open challenge window. Also, when we access that open challenge window at the same time, we see different challenges hosted by others. Almost like we are now pooled into different communities using the same game. What happened? how to fix?

[Erik2]

You have both updated to v9?

[GabeKnight]

You can't mix PC and Mac versions anymore Legacy Patch - v8.6.9 (End of Mac support)

[Grendel88]

Well. I'm a Mac and he's a PC, so we can no longer mix in multiplayer, so in the vernacular that would be called "a bummer".