This bug was seen on the iphone SE (first generation).
The bug is that the texture pack (shaders mod) downloaded from the outside is applied, the app is closed with the world open, and when you return to the app, the textures are randomly replaced.
I tried it multiple times, but it seems that there are some patterns depending on the block as to which texture will be used.
I'm sorry if there is a problem on the shaders MOD side.