The Simpsons is an iconic part of television and has been going on for over 30 years now. In all that time, there's bound to be inconsistencies; especially with cartoons. After a rewatch of The Simpsons (or multiple), there's a few different inconsistencies which start to crop up. Some of them multiple times.
This list ignores the Treehouse episodes, and the flash forwards, as they're not usually considered canon. Flashbacks are thought by the fanbase to be canon episodes, so they are under consideration here, although to avoid just making it about them, the obvious things have been left out.
The episode That '90s Show does throw a fair few plot holes our way, but they're not ignored by the fanbase. On the contrary, they're one of the biggest bones of contention in the modern era.
Still, other little plot holes do slip by. Either because they’re only noticeable having watched two (or more) different episodes, or because they’re minor details in a story overall.
The Simpsons is one of the most comforting shows to watch over and over again though, so these plot holes can pop up a lot if you settle down for a binge.