I had a 2020 return that did that a few months ago, and I disable error checking (even though there were no errors) and it worked. It might be worth a try.
There is another post on this forum and something else had worked for someone else, but unfortunately the search feature on this forum is useless.
If you have an attachment thats too big this will happen.
Make sure your program is updated (you may want to run Refresh/Repair updates) and try transmitting from the EFCenter, rather than from within the client file
I had the same thing this morning on a 2019 return. No errors, went thru all the little steps, and ended up, right where i started, did the review again.... tried 5 or 6 times. then did an update on that year's program, and worked like a charm.