ID help request: strange mystery bird, Harry Griffen Park

While we were waiting for the Lucy's Warbler to show up this
morning, a bird appeared that matches nothing I know. It was in open
view in eucs about 50' from us, moved around a little, then disappeared.
I took notes on all the details we noticed: Roughly tanager size
overall. Bright yellow bill (tending to yellow-orange); bill small and
thick – perhaps similar in size and shape to scarlet tanager's. (Keith
thought the bill was longer.) Very bright yellow undertail coverts
(perhaps extending up lower belly). Yellow (or yellow-green) suffused in
dark (maybe olive) uppertail coverts/rump area. Except for the bright
yellow below, the front of the body was white or light gray. Two
distinct white wings bars on dark (maybe olive) wings. Face relatively
plain, dark eye; Keith saw thin eye ring.

Any ideas? Thanks. (Lucy's showed up at 9:35AM.)

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Sara Mayers
Point Loma, San Diego
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Sara Mayers
Point Loma (San Diego)
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Source: SanDiegoRegionBirding Latest Reports