I've noticed vertical stripes of blocks appear at random in a few of my worlds - one I just play locally, and one that I host on the "official" Bedrock server on Ubuntu. (https://www.minecraft.net/en-us/download/server/bedrock/).  Please see attached screenshot.  These blocks do not behave like real blocks - I cannot pass through them - they block my movement, but they do not have any breaking animation.  In the case shown in the screenshot, breaking the grass will also cause several of the dirt blocks above the grass to disappear.  If I break them all, they will re-appear, sometimes invisible but still impassable until something (a block update, maybe?) makes them reappear.  This screenshot shows my latest discovery of this.  I've also seen the blocks be entirely leaf blocks, in this basic pattern but with a couple differences, and a mix of mostly oak logs with a few leaf blocks.