I have set up point symbology in Pro to "allow symbol property connections" and connected the picture marker to joined attachment table BLOB field. This will draw the point using the picture that it has as an attachment.

However, when I publish a mapservice with this data, the markers show as generic picture icon:

Documentation says picture marker symbols are allowed in mapservice, but can't get it to work.
Are attribute driven picture markers not supported, or is something else going on here?
Thanks for any insights,
R_