If Savitar's prison was anything like Wally he should have had been suffering not seeing the timeline. If he was able to see FP that would mean he was able to free himself from the prison and was just runned around the speedforce. Even if Savitar was able to detect a change in the timeline shouldn't he be seeing the year he was locked up in and not 2016? I know I am overthinking it but it is a plothole that is weird because the two episodes were we learned about the prison and how it looks are only a week apart.