Hi, thanks for the update,
It seems you might have the same issue as this person. However I’ve not had the pleasure of a AMD video card so no experience with getting it to cooperate on Manjaro. Perhaps (this is what I would do first ) a reinstall of the driver (see here) repairs this issue. Or a more knowledgeble user comes along and points you to a solution. Have you searched this forum? This post might be of interest or might point to a solution in your situation.
Edit: also this post, a faulty cable was the cause, but less likely since it worked before.