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@David Inglis try to disable "Check for publisher's certificate revocation" and "Check for server certificate revocation" in Internet Explorer and restart all Studio instances as a primary workaround. Are the DDCs in the same zone/physical location?

Yes DDCs are on same LAN. Using Studio directly on DDC is equally painful. Thanks will give your suggestions a try.

Google mmc.exe.config regarding PublisherEvidence. Check your Internet/PublisherEvidence. Check your internet/proxy configuration.

Sorry everyone, but these recommendations (while very, very common) are not the best way to tackle this. It is limited in scope (e.g. mmc.exe.config will fix only MMC console). Instead, you can use a Group Policy to disable CRL checks for whole machine: https://www.citrix.com/blogs/2012/06/05/slow-web-interfacemmc-console-crl-explained/

@Martin Zugec Can’t believe I have overlooked this blog post 🤭. Thanks!

Thanks all. My issues are more moving around within Studio rather than waiting for it to start. Removing all proxy settings (and a reboot) seem to have made an improvement - though could of course just be the reboot. I will go through your recommendations Martin - thanks.