Custom Pages Domain stuck on "Inactive (Requires DNS Setup)"

Hi, I've set up a pages site, and have just hit the button on our DNS to CNAME to our pages.dev domain and being the transfer process. I've done this successfully before with our main domain, and am now just replicating what I did before with our sister site. Using nslookup.io or whatsmydns.net to check propagation I am seeing everything updated worldwide - I only ever set TTL at 30 seconds with our DNS providers so problems like this are minimal. This includes when checking against cloudflare's own records on nslookup.io - everything is showing that I have the CNAME set up appropriately, and I click on the link it shows and I get to our pages site. But when I go to the "custom domains" tab I get the orange inactive indicator, and if I press "check DNS servers" and wait, I'm still not getting anything back. I know it can take some time, but, given everything is propagated elsewhere successfully and this ran within a couple of minutes every time when I have done it before, I am not sure what the holdup is. In the meantime our site is necessarily down in the interim as DNS is the one thing I can't work around on any of our servers. Can anyone advise please on what I might need to do? Thanks!