Please note  that your bug  affected versions  does not  reflect  the Beta version  4 bedrock  that is presenting a problem . 

My Minecraft PE bedrock files are stored externally.

After the 1.16. 0.58 update from 1.16.0.57 only 19 of my 31 Worlds open on the Minecraft play menu.

I know for a fact the world's aren't corrupted as I also did a backup and tried accessing in the files as per the back-up.

This rather looks like an error in the code in Reading files that were created in non beta versions dating back the last year.

Important note: during the upgrade a delete data message appeared as conventional with certain upgrades installations or deletions. The menu did not present the usual option to retain or delete associated data but rather proceeded without prompt. I fortunately noticed same and pressed cancel deleting data.

 Kindly assist at your soonest convenience