404 for some images with Backblaze B2 Content Through Cloudflare CDN

Hello,
I have setup a link between Backblaze and Cloudflare CDN thanks to this alliance. I also have setup seom cache in Cloudflare.

https://help.backblaze.com/hc/en-us/articles/360010017893-Delivering-Backblaze-B2-Content-Through-Cloudflare-CDN

For some reason, I get sometime 404 errors for some existing images and sometimes not.

If I wait and retries it cames back again to normal…

What do you think I can do ? Where can I debug this ?

I follow soemthing similar to this :

https://gist.github.com/charlesroper/f2da6152d6789fa6f25e9d194a42b889
https://gist.github.com/davelevine/795df9e7d14aabda4d1bdfc6b66158bc