You must be having a matrix question with scale point number greater than 3.
So according to iQ(ExpertReview), matrix question is itself not a mobile friendly question, even if you check or uncheck the mobile friendly checkbox. You can change that question to multiple single choice question to avoid that ExpertReview warning

Ok, thanks rondev . Still doesn't sound logical though. How can a question flagged with "mobile friendly" be NOT mobile friendly... isn't that a bug?

https://www.qualtrics.com/community/discussion/comment/26837#Comment_26837I agree with you. But from what I understood is, when we are checking the mobile friendly checkbox, it means that we are making our question mobile friendly with respect to UI. But the expert says something regarding to response rate. Check this

https://www.qualtrics.com/community/discussion/comment/26838#Comment_26838OK, then IQ should not label it as "optimize for mobile" but just plainly "avoid matrix questions". Because a matrix question on a mobile doesn't even look like a matrix but looks like separate multiple choice questions.
I'll make a product idea out of this I think :D