The glow squid loses its glow when hurt, which means it is no longer emitting light and should be properly shaded.

This is more apparent in the latest beta. Because of the fix for MCPE-121754, there is little difference between glowing and non glowing glow squids during daytime, as the sunlight is already really bright.

The addition of the ambient shading when hurt would help differentiate and properly display that it's no longer glowing.

Notes: The glow squid texture is a targa (.tga) file, which means it allows for a separate alpha channel. Having it fully black will remove the shading, while having it fully white will make it shaded at all times. A way to fix it, although not an ideal one, would be to use separate textures for its glowing and non glowing state.