This issue was discovered when testing MCPE-178015

Relates to MC-263062

billy.sjoberg said, the block doesn't fall until a neighboring block is updated.

When the sand or gravel is generated floating it never falls no matter how many random gameticks pass.

However, when the suspicious sand or gravel is generated floating it will fall after some random gameticks which is also different from Java Edition

Analysis
Here is a video that shows the issue MCPE-178020.mp4

Sand generated floating	Sand suspicious generated floating	Gravel generated floating	Gravel suspicious generated floating
not fall	fall	not fall	fall

Steps to reproduce:

1. Import world ( Suspicious gravel and sand bug.mcworld ) and enter
2. teleport in coord

   /tp -416 66 -205
   

3. Wait two minutes

Observed behavior:
Gravel and sand suspicious block, falling when passing some random gameticks

Expected behavior:
Gravel and sand suspicious block, never falling when passing some random gameticks