Warped Fungus and Crimson Fungus grown under any block will cause that block to break and disappear forever the picture below is an example.
Notes from MCPE-65757
At y=121, you can place warped/crimson fungi on their 'dirt' blocks, using bone-meal, they will sometimes clear out some bedrock blocks above them. Another way to fool it is putting warped/crimson blocks between the fungi and the bedrock and it let's it grow still.
Thank you for your report!
We're actually already tracking this issue at MCPE-65661, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
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