Show/Cartoon/Anime: Star Trek The Next Generation
Lull: S1-2
Rebound: S3+
Did it stick?: Yes
The first couple of seasons of Star Trek The Next Generation are pretty bad. Riker grew a beard and things got better.
Writer changes may have also helped.
https://tvtropes.org/pmwiki/pmwiki.php/Main/GrowingTheBeard
Does it count if the show started poor and got better? That is the trope that you quoted, which is fairly common (for instance, like The Simpsons not really hitting GOAT status until about Season 3 or Seinfeld getting over its clunky first season). What the OP is after is rarer.
The Office somewhat recovered in Season 9 after Season 8, although that was mostly in terms of just creating satisfying conclusions for the end of characters' stories.