Transparent header issue without changes

We have a transparent header configured with a single color logo. When the user scrolls down, the header becomes opaque (white background vs. transparent) and displays the multi-color logo.

It’s been working fine for 2-3 years and has suddenly started displaying both the full color and white transparent background logos on top of one another.

I can’t figure out what has changed. I think we are on the latest version (3.20) and have been for more than 12 months.