It’s definitely not confirmation bias, though I guess it’s not out of the realm of possibility that it’s just a coincidence.
The most recent example - that triggered this OP - is a Spanish station that I listened to for about a year, when I was into learning Spanish. I noted at the outset that reception was shaky and consciously persevered (after failing to find a better station) because I was motivated to get more exposure to Spanish. And I definitely noticed that reception became perfect after a while, with the exception of a certain stretch of my commute. And now, having lost interest in recent months, I only rarely tune in and when I do, lo & behold, it’s back to the fuzzy reception that it had when I first began listening to it.
This is not the first example that I’ve encountered, but it’s the most recent and the one that I paid the most attention to.
But it’s not out of the realm of possibility that the reception happened to get better and worse at these times for unrelated reasons. (I only listened to that station on one radio, so I don’t have a basis for comparison.)
The radio is not all that old - it’s what came with a 2000 Chevy Prizm.