I'd recommend doing your daily quests, that will give you around 1000 free experience. Replay the easy nodes if you need to in order to do so. Also, you can replay all the old nodes to acquire the gear you need to get your characters to higher gear tiers. There are a lot of "gates" in this game which can only be passed by slowly improving your team. Once you get to level 50, you will unlock mods, which are a game changer. Upgrade mods with speed on them (and make sure you have at least 5 arrow mods with a speed primary, that you can switch to whatever team you're using).
TLDR: Do dailies, gear up your characters, and you'll eventually be able to pass whatever walls you're hitting.