Julian, hi and welcome to the site! You're describing a common dilemma. Basically, you should feel free to move forward and work on other stuff even if you haven't perfected certain skills like a particular chord or tricky chord change.
Few rules to guide you though with your practice:
1) Practice/play at a speed so that you hardly ever make a mistake. If you are making lots of mistakes, then keep slowing it down until you don't. If you can't play a chord in time at all because you can't get the fingering right fast enough, then don't worry about making music with that chord, work on just the correct fingering and getting the chord to play cleanly first. When you can do that, then move on to playing it with rhythm and in time.
2) Don't build on mistakes. If you're going to learn a song, that has a new fingerpicking pattern AND a chord that you have a lot of trouble playing, don't try to combine all that together and work it all out at once. Recognize that knowing the chord is a prerequisite to learning that song, and master it first, then learn the fingerpicking pattern, then put it all together. Divide and conquer will move you ahead the quickest.
Keep in mind it takes time for new skills to sink in. So feel free to work on several different lessons in a practice session, rather than just spending an hour trying to learn one chord. If you practice something very slowly and cleanly for 15 minutes, then come back to it a day later, you'll probably notice a marked improvement. Sometimes your brain gets bored with too much repetition, which is why you can actually start playing something worse than you were a few minutes ago if you sit with the same task for too long.
Good Luck!
