Can't Duo with anyone even though I could duo with them before. Bug Patch 7.1

It's not a network issue, but for some reason my client says whenever I try to invite someone that they are ineligible to join me, even though the people I invite are either the same division as me, or just one division above me (silver) or they are unranked but I know they were silver last season. So I don't know why this is happening but it is making me very sad :( Please help