As many might have noticed. OpenCL will currently work on multiple same generational GPUs. But currently (as from 18.30 driver versions I noticed) legacy and pal platforms will not work together. This could be related to upstream changes to the OpenCL spec (2.x). So probably not something you could blame AMD for (But I’m sure with access to source they could find a workaround). Little surprised this issue hasn’t had much of a mention.
So, to get legacy, pal (VEGA, NAVI etc) to work together please try this patch.
Also read about the issue here and download the patch.