.dev domain never works with Cloudflare Pages

I have two domains, also.dev and also.wtf, that I want to use exclusively for Cloudflare pages. Both use Cloudflare for DNS.

also.dev and any subdomain like test.also.dev never work when added as custom domains for any Cloudflare pages site. also.wtf and test.also.wtf work fine. When I go through the “Set up a custom domain” process, I can see that the record is always added to the DNS configuration for the domain with a proxied CNAME. But in the Custom domains screen, also.dev domains immediately show “Inactive (Error)” while also.wtf domains appear in the “Verifying” state.

After adding the configuration, loading https://test.also.wtf will start working quickly - even while still in the “Verifying” state, but https://test.also.dev will only ever return “Connection timed out Error code 522”. The error is returned is less than 400ms, so it doesn’t seem possible for this to actually be a real timeout which Cloudflare suggests should take at least 15 seconds (https://developers.cloudflare.com/support/troubleshooting/cloudflare-errors/troubleshooting-cloudflare-5xx-errors/#error-522-connection-timed-out).

The only difference between also.dev and also.wtf that I can see is that .wtf is using Cloudflare registrar, but .dev isn’t, as it isn’t supported.

I’ve tried configuring these domains a few times over the past year, always with the same errors. What do I need to set up so that also.dev domains work with Cloudflare pages?