What is the domain ?
Looks like something wrong with you SSL certificate or instalation
It should not be showing the certificate request contents ?
The problem is only on mobile
tried both Safari and Chrome
Works fine on my mobile
This is strange, I clean my cache and try again, don't work on chrome Android, also on safari iOS, I check my system and it's up to date 16/09/2021!
Maybe you need to update your system to see the bug.
I updated to iOS 15.0.1 still can not see any issue
I dont know what the Additional Certificates (if supplied) are
But yes if they are expired and if they are used
They probably need to be renewed
You could check with the SSL Certificate provider