Bedrock Edition does not support partial alpha transparency in skin layers, resulting in missing or incorrectly rendered semi-transparent elements like glasses. This is not affected by graphics settings, resourcepacks, or even the newly introduced Vibrant Shaders.
This issue is not present in Java edition, where partial alpha transparency renders correctly on skins. Attatched are images, and the skin used to replicate the issue.
This issue is being tracked at MCPE-31500.