Copper ion and ascorbic acid undergo some complex redox reactions that evoke Fenton chemistry.
See, e.g., Zhou et al. RSC Adv., 2016,6, 38541-38547 (Link
They identify dehydroascorbic acid, 2,3-diketogulonic acid, and L-xylosone as downstream ascorbic acid oxidation products.
I note that copper (II) ascorbate was long ago considered as a food preservative, but with a drawback:
"Dehydroascorbic acid may become oxidized further to CO2 and other byproducts [probably those mentioned in the more recent article]. The formation of these secondary metabolites renders the use of copper(II) ascorbate unsuitable for clear beverages, since these types of products assume a slight reddish-brown hue
after extended shelf life." (emphasis mine)
(See, Graf, E. J. Agric. Food Chem. 1994, 42, 1616-1619, Link
"Reddish brown hue" seems pretty consistent with what you're getting. So, I'm guessing the copper ions in your treatment are catalyzing the extensive oxidation of ascorbic acid, rendering a mixture of organocopper complexes that add up to some reddish brown muck.