GLES backend is too strict right now about registering/unregistering functions compared to Metal/Vulkan. See https://github.com/flutter/engine/blob/1cf2e0a603c7d1db940378f23045a539abd5053e/impeller/renderer/backend/gles/shader_library_gles.cc#L121-L125 and https://github.com/flutter/engine/blob/1cf2e0a603c7d1db940378f23045a539abd5053e/impeller/renderer/backend/gles/shader_library_gles.cc#L144-L148