I’ll take a different direction with this concept, and list the missteps from each installment which were the most inconvenient and/or caused problems for the other movies:

ANH: The Clone Wars, a throwaway reference practically guaranteeing a prequel trilogy filled with faceless cannon-fodder.
ESB: Luke and Leia’s kiss, souring the sibling retcon.
ROTJ: Killing off all the major villains, leaving no substantial threat for future sequels.
TPM: Midichlorians, dissolving much of the mysticism of the Force.
AOTC: The Sandpeople slaughter, ending all sympathy for our protagonist in the middle of the story.
ROTS: The youngling slaughter, turning Anakin from merely unsympathetic to someone that Luke would surely never try to redeem, and by extension poisoning the entire purpose for the prequels.
TFA: Destroying the Republic Capital, ensuring another repeat of Rebels vs Empire.
TLJ: Hyperspace ramming, which in concept is more effective than capital ships, shields, and Death Stars.