Same issue for me. I have been downloading my world weekly for backup purposes and for a few months now I have been unable to download my realms world. This also prevents me from transferring worlds between my PC and Xbox as you can't import worlds from storage on Xbox.
Can confirm I am now having this issue, but my world got to ~1.6GB before being unable to download.
Yes, it does move blocks using a piston, so I guess MCPE-33072 is the issue.