Hi,
It looks like there are some episodes of adventure time season 8 that are listed as part of season 7. I'm basing this off of wikipedia though so it may not be accurate. It just seems like season 8 is much shorter that it should be. I believe the "preboot" and "reboot" episodes are the appropriate break between seasons 7 and 8
https://en.wikipedia.org/wiki/List_of_Adventure_Time_episodes