I use bedrock, not preview, and had similar issue. My worlds are gone. They routed me to this thread
MCPE-218647
Hey Sean,
Had this issue as well after the update. Worlds I had just vanished. I even made duplicates on both my internal and external storage since this exact instance happened on my previous world I had for 10+ years.
I even tried clearing the xbox local cache in “manage games” to see if the cloud backed up my world but I believe it was too large (500+MB). If anyone from Mojang can give any insight how to recover these please let us know.
@Sean
Unfortunately I tried clearing the cache and the uninstall game method but the cloud saves are from older versions of the world. It was probably a local save and me uninstalling it just wiped everything as a whole. My only hope is if Mojang has a major archive of it somewhere but I’m accepting it’s all lost forever 😿