This usually does the trick for me if it stalls out:
Close out your project, and sign out of Rush and Creative Cloud.
RESTART YOUR COMPUTER, and make sure you don't have any memory-intensive ("RAM-hogging") apps running while you're starting up (I never run Photoshop, Illustrator, or Microsoft Office apps while working on videos).
Sign back into your Creative Cloud Desktop App.
Hold CTRL + SHIFT buttons while starting Adobe Rush - this will tell Rush you want a "fresh start" without losing your projects; it will open the Starter Tutorial like you were starting for the first time - simply close the tutorial, and your projects will be available.
Open your project, and BE SURE TO WAIT for it to FULLY SYNC. Then try editing and/or exporting, and you should be good to go... but just in case:
double check that any Adobe Fonts you may be using are activated and connected
re-add any missing assets to the project bin
Last Resort: DUPLICATE the project and try working from the fresh copy.
Hope this helps!
Anissa • @anissat
Hope this helps! Make sure to press "✔ Correct Answer" on this post if this answers your question. Happy Rushing!