We may not be able to pinpoint the issue, but with a complete history of how you care for the tree, and possibly examining the leaves, we could suggest things to try next summer before you decide on replacement. The tougher-to-diagnose possibility is a genetic variation in how much fall color develops on individual plants. This is why shopping for a replacement is best done right now so you can judge colors the best. Here is the OSU Landscape Plants page for vine maple, Acer Circinatum: https://landscapeplants.oregonstate.edu/plants/acer-circinatum A quote “Prefers moist, shady situations, but tolerates sun.” Compare those you see with good color and those without. Is the amount of sun a predictor of fall color? Here is a blog from the Washington Native Plant Society about the vine maples and some named cultivars: https://www.wnps.org/blog/vine-maple-variations Here is the PNW Handbook page for anthracnose on maples: https://pnwhandbooks.org/plantdisease/host-disease/maple-acer-spp-anthracnose Note the cultural controls. The chemical controls include only one for homeowners, so you may want to hire a certified arborist to make applications. Also note that the time to apply is spring. Have an arborist now diagnose your plant if you will consider spring treatment next year. We can help with some troubleshooting of care for the tree, what to look for next summer, and looking at the leaves now, possibly determine if disease exists. Once leaves begin the fall coloring, though, it is especially hard to tell disease from things like sun scorch, frost, and normal fall decline. Check with the county Extension Service Master Gardener Volunteers for office hours. Bring in leaves in various stages of green and color. https://extension.oregonstate.edu/mg/metro/have-gardening-question