I reproduced this problem using a browser on Windows. So, not curl specific either. See below.
But, if they are willing to have users suffer having to reload the page they could get a cert using the DNS Challenge. Personally, I wouldn't want anyone to see the failure but we don't know how broad it is. I have reproduced using several different IP addresses but all in the USA, for example.
This is well beyond a question of getting / using certs. Still, I would be curious to learn a solution to more quickly help people. We've seen this a number of times now.
Here are example pics using Edge on Windows 10. I used a private window and reproduced this twice. Once with http:// and again (below) with https://.
First request
Immediately reloading page gets their home page
