I had the same issue migrating an app off of Render (they also use Cloudflare for app routing).
Cloudflare would refuse to route to my new IP for hours on end. Incredibly frustrating and I almost pulled my DNS off of CF as a result.
I was able to work around it by disabling the orange cloud for the domain for a couple hours, then turning it back on, which must have reset some sort of cache on CF's end.
Ultimately, it's not a DNS issue, it's an internal CF routing issue - it only happens with CDN (orange cloud) on. It seems CF's just caching the orange cloud's original route (via the SaaS provider) way too long internally somewhere and it's not being cleared when the route is changed off of the SaaS.
Cloudflare would refuse to route to my new IP for hours on end. Incredibly frustrating and I almost pulled my DNS off of CF as a result.
I was able to work around it by disabling the orange cloud for the domain for a couple hours, then turning it back on, which must have reset some sort of cache on CF's end.
Ultimately, it's not a DNS issue, it's an internal CF routing issue - it only happens with CDN (orange cloud) on. It seems CF's just caching the orange cloud's original route (via the SaaS provider) way too long internally somewhere and it's not being cleared when the route is changed off of the SaaS.