Grass changing to dirt doesn't happen immediately. It's a random event that typically take several minutes to occur, so this may be working as intended. However, if you're seeing a lot of it within smallish spaces or it persists for a long time, this may be an issue. Try to give more details: What's the most examples you've seen all in a local area? Were they completely buried or did they just have a block on top of them leaving them partly exposed?
Edit: Also, what type of solid block is on top of them? Some solid blocks (glass, grass path) are transparent; grass will actually grow on dirt beneath them.
Thank you for your report!
However, this issue is a Duplicate of
MCPE-23602.If you have additional information, please add it to that report.
Please search before reporting, as it's likely that one exists already.
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