If neither of the jumps is in combination, I think the jump with the higher base value is treated as a +COMBO (not entirely sure though - it could be that the planned jump combo, usually the opening one, is treated as a combo).
According to the tech panel handbook, "If there is no second jump in a jump combination, the Technical Panel identifies
the intended combination during or after the program. If there is no clear way to identify the combination or the solo jump preceded by steps (steps or no steps in both cases), the Technical Panel will decide which one is the solo jump and which one is the combination in favour of the skater."
I understand "in favour of the the skater" to mean that if one of the two solo jump attempts does not
require -3 GOE, they would call that as the solo jump and the other one would be called +COMBO and get -3 anyway, just for having no combo whether there's anything else wrong with it or not.
Of course, in a SP a solo jump with
no preceding steps is supposed to have the GOE
reduced by -3. But the final GOE doesn't have to be -3, if the jump itself was really good and started off positive.
A SP required jump combo with no second jump attempted is required to have a final GOE of -3. That's now the only automatic required GOE (although it's very rare for jumps with falls to get higher than that).
Judges should give -3, but of course you still have many judges who'll still give -2 or higher (it's not automatically -3's across the board).
It should be automatic in the sense that it's required (SP jump combo with no second jump), but the software doesn't force them to give -3.
The -2 is a mistake on the part of the judge, but it's easy to see how that mistake could occur. The judge might see a step out of a jump with immediate preceding steps/moves, or a poorly landed jump with a gap between the takeoff and any preceding steps, and conclude that this is the solo jump and deserves -2, so that's what they input in the computer. Then the skater does another non-axel jump with no combo, successfully or not, and the judge marks it accordingly. At the end of the program the tech panel decides that the first solo jump should count as the combo, but the judge forgets to go back and change the GOE to -3.