(answered on Matrix but adding here as well for anybody else with the same question)
I think this stopped working in a recent release of Galaxy, maybe a bug, but as a workaround we now have a tool you can install that will convert qiime’s qzv outputs to html that can be viewed directly in Galaxy, which would also help in the case your Galaxy server is behind a firewall (the display link would not work in that case).
Here you can preview the tool on Galaxy EU
It’s an extra step for users, and ideally in the future the qiime wrappers will output this directly, but perhaps it’s helpful for you.