The page takes great pains to explain things, but omits a frame of reference for this speed. I’m guessing it’s sun-relative, but it could be relative to its take-off on Earth. Does anyone know?
https://science.nasa.gov/mission/voyager/where-are-voyager-1...
You're right that Earth is catching up to the Voyagers during part of its orbit for several months in the early part of the year (and you'll see that reflected on the Mission Status page). Consequently I used to wonder if Voyager 1 would reach 1 light day from Earth 3 times - the first time, then a second time when the Earth distance decreased, and then a third time when distance increased again!
If you scroll down on this TheSkyLive page, you can see a graph of Voyager 1's distance from Earth over time and it's an up-sloping ripple instead of a straight line. You can play with the markers to zoom in and see that the catch-up phase happens in the early part of the year:
[0] https://eyes.nasa.gov/assets/dynamic/dynamo/sc_voyager_1/now...