Placeholder ID. Second hybrid YRWA frequently the suet feeder in my yard this weekend. The other can be seen previously in my observations and lacked black mustache this bird has. This ID Myrtle x Audubon's seems most likely.
But I can't explain the black mustache this individual exhibits, that's not a YRWA trait as far as I know. YRWA does hybridize with other Warbler species but documentation is hard to find.
Time to call in the experts on this one.