Sorry to hear you’re having this problem, I’m sure we can get it sorted out for you.
I’ve had a go a reproducing it on an iPad here - I created a new blank pptx from smartoffice, saved it to dropbox, then opened it, edited and saved it, and it all seem okay - I didn’t see bad delays or freezes.
Can you think of what I’m doing differently to you? Is it dropbox you’re using or one of the other providers? Does it only happen with some powerpoint files, and if so would you mind sending us one that it happens with (email address is email@example.com ).