Hi,
So I'm not intimately familiar with this use case, but I have a couple of pointers.
Did you add X-Frame-Options to the exposed headers in the System setting? (This is more of a guess than a recommendation 🙂 .)
Silent refreshes have some other issues. This github issue may be of interest: https://github.com/FusionAuth/fusionauth-issues/issues/521 . It points to a workaround: https://stackoverflow.com/questions/55859793/is-prompt-none-for-silent-refresh-in-a-spa-possible-with-fusionauth-and-its-prov where there's actually a suggestion to tweak the web.xml file.
Finally, if you have a support contract with us, please open a ticket.