After a long time without playing, I started STO again and all my episodes are resetted. The game wants me to play one of the Klingon Episodes, but I'm already at level 33 an played "Rapier" as my last mission. I only can replay missions, I already played... but the next mission after "Rapier" isn't startable. What's happening there?
Its all part of the new storyline progression system adopted to point newer players in the right direction and try and cover content gaps.
to be able to get back to play the next mission after Rapier you will need to skip or run the previous missions in the journal you have yet to do and crucially make sure you have leveled enough to qualify for the next mission.
There is no option to skip anything. All "Skip"-Buttons are grey. Just the replay-button for played mission is usable.
If the Skip button is greyed out - and you only have the Replay button, it means your mission progression WAS NOT reset. Skip being greyed oout means the game knows that character already played the mission at least once.
That said, they did add a minimum level requirement to the missions; so if our character is below that level, you'll need to get to that level to access the mission you want.