Whenever we have bedtime silliness it usually comes down to overstimulation/overtiredness, illness, or needing some more connection/Mummy time. It comes and goes in phases here, I know that's not much help but wanted to reassure you that bedtime isn't ruined forever
maybe you could just give EBT a go as a one-off? Early dinner for everyone? Sometimes they just need it that one time to catch up. Or if you don't think it's that, then the other thing that helps here is being completely solid about 'the rules', whatever they are. Here it is 3 books, a song and then lights out. Any messing, we say goodnight and leave. DD will then usually call me back in but that's the end of the nonsense.
Just as another thought - do you use blackouts? Any chance the seasons changing may be having an effect?