added key signatures disappear

I am new to Musescore. I'm creating a score with multiple parts and a key change about halfway through. I put a double bar at the key change and successfully dragged the new key to the work I had done on some instruments. When I reopened the file after a few days, the key changes had disappeared, as had the double bar. Now when I try to put it back in, I drag the new key signature to the right bar, but it won't take. I can put the new key in other bars, and reinsert the double bar, just not the new key where I put it before - any ideas why this is happening? Am I just missing something that would let me see what I've already done? Otherwise I've had no problems.