Please post those screenshots of the mission, your champs and what their gear looks like.

Thank you.

I'm having the same issues with some of the gears missions and I can't go to the next levels!!

Any helps ??

Thanks 

can you take a screenshot of the mission you're trying to do and the gearing on your champions?

This finally cleared... Not sure if was the exact reason, but it happened just after I filled missing Artifact slots on one of my Champions that had the required 4 Life Artifacts of 4* or higher... but had no artifacts in the other two artifact slots. When I put random artifacts in the missing artifact slot... I magically cleared the Mission.

I think the problem was... it doesn't say anywhere, 'of Champions with all Artifact slots filled'... so there was no reason to think that was a requirement. 

As mentioned... I wasted millions of $ selling and re-equipping artifacts until I figured it out... and worse yet - time not being able to complete the missions that came beyond it.

Tough to say without seeing screenshots/visuals of the mission and gearing whether or not that was the issue. I'm not aware of that being a current bug with the Arbiter missions (or any outside of claiming her when 75/75 or more is reached)