This old world my server has been playing for a while was recently converted from Java 1.14 to Bedrock 1.16.200. (Prior to Bedrock conversion the world was updated within the Java client to 1.16.4) These unknown blocks fill voids where air would have previously been in some holes above ground and all holes below ground. This must be some kind of block ID issue that came up during the conversion.

Does anyone know how I can convert all of these unknown blocks back to air? I haven't been able to find any hints online, not many people are encountering this issue. 

We switched, all purchased Bedrock, and set up a new server on Realms so we could include more potential members. So going back to Java isn't an option for us unless by the grace of Microsoft Java gets crossplay.

Resource pack: Default

Behavior pack: Default