I was so surprised and bummed when I discovered this was a thing. My wife and I started watching the original Beverly Hills 90210—a sort of ridiculous snapshot of American pop culture in the early 1990s—on some streaming service, and after a few episodes I noticed the music was just...super wrong.
Reading online, I learned that a lot of the original music had been licensed only for the original run of the show, so even when it went to DVD in the early 2000s they had to remove a whole bunch of the original music. It's terrible on two fronts: one, the show is an awesome snapshot of 90s music, with tons of great stuff featured both as background music and in extended live performances, but they cut whole scenes and entire episodes that had too much of it, and two, whoever managed the process of picking replacement music clearly did not care at all, and used awful generic music that sounds like it came from a file called "BeachRiff.aiff" on a $29.95 CD library of royalty-free 60 second stock music samples.
I admit to finding a source of video files patched together from various sources with the original soundtracks intact, and it's simply MUCH more enjoyable. It seems, though, that some episodes of live performances are lost to time—or at least lost to the corporate owners who'd rather sit on the tapes in a warehouse somewhere than make them available.