Are you kidding ?
I have enough trouble knowing what mode I'm supposed to be in when I wake up !
Aah, ...seriously, though, ...I should have explained my "theory" a little better ...and I do NOT know
...what mode it's supposed to be it when it's powered on in a vertical orientation?
I'm sure, however, that one of the Line 6 guys will provide that info as soon as they're back on line.
My earlier reply was (and indeed, this one is) simply drawn from my experience of other such systems ...and was (is) only submitted with a view to possibly providing some interim reassurance.
That ongoing experience to which I refer has led me to largely ignore any such display anomalies that might immediately appear upon the initial power-up of any firmware-based gyroscopic system for inertial guidance.
In other words, if your ears tell you that your StageSource L2T eventually settles on a "sound" that's appropriate to its orientation, I reckon that all is almost certainly well, unless the Line 6-ers come back to us from their weekend and say otherwise.