Looking at both pics,looks like a pellicle which most likely means wild microbes in the fermentation.
Sour/tart may be from lack of sugar.
I am assuming this is store juice or orchard juice for drinking, not cider making blend. Not uncommon for a tart finish as there is no sugar and low bitter/sharp/tannin flavors to balance the acid.
I definitely would. Retaste once cold and carbed. You can consider adding 1-2 quarts of juice of choice if keeping cold(preservatives are ok at this point) at kegging, or add a splash of juice to each pour if it's still too tart.
Keg it. I’ve had a pellicle several times With pressed juice cider. I dosed with campden before kegging. No off flavors that I detected. But once I saw the pellicle I didn’t let it sit for too long.
I had that once, didn't know about oxidation back then and the cider started out "sour" and got worse over time, and eventually became undrinkable. I actually kept a little and made mustard with it and that was not bad.