This also affects Seagrass, Kelp, Coral, and some other blocks if they are in water and next to glass on the east west direction
If you are on an older iPhone, try lowering your render distance (Click settings, then scroll down on the left side and click video, then scroll down on the right side and drag the bar that says "Render distance" so it is lower than before).
Older devices may have issues when new updates come out or just as they age.
I tested this, it seems to only happen on mobile, and not windows.
EDIT: Apparently it also happens on Switch, so mobile-like platforms probably are the only ones with the issue.
If you smelt coal ore into coal, it does not stack, and there is no way to fix it but making it into a block and decrafting it back into 9 coal.
If it's fear of mobs, try placing a lot of slabs on the ground outside your safety box.
This issue is happening in 1.13.1 for me