I seem to recall that there are some sim limitations to using WASM gauges as pop-out windows, and as we are using a mixture of WASM and HTML/JS gauges for the EFB, there may be some limitations encountered when using our EFB as a pop-out window.
This isn't something we have looked into for quite some time though, so it may have changed in recent MSFS updates. We'll log this on our internal bug/feature request tracker to investigate ahead of a future update.
Mark - Just Flight