iOS10 App & Let's Encrypt SSL "Unable to connect to server at this time"

I am on latest version of Nextcloud 11 Snap on an Ubuntu 16.04 server.
I have an SSL certificate from Let’s Encrypt. I used to set up a free hostname.
So I have

My Androids can connect with no problems, my ipad and iphone get the error message
"Unable to connect to the server at this time"

Apparently iOS10 does not like my SSL certificate.
Is there a workaround other than switching back to http?

RESOLVED: Latest Nextcloud app update resolved the issue. – Thank you Devs!

I am still having problems using Let’s Encrypt but as ddns service, nextcloud 11.0.3 and Nextcloud for IOS 2.17.1.

Sometimes, it works, but most of the time get An SSL error has occured