I wouldn’t expect any software to read the panose numbers for variable fonts. The only software that uses the panose are Code editors that will only allow “proper” mono spaced fonts.
Did you set the “isFixedPitch” parameter in the font settings?
Ok, so I set the “isFixedPitch” parameter and as the warning says it set all of the widths according to the width of the space character (auto width). The widths (per master) were already monospaced so no actual changes were made. The Variable font works fine and there are no fails from the Fontspector. It is even not complaining about the PANOSE anymore which I did not set, so I guess that “isFixedPitch” parameter takes care of PANOSE also.