I fixed it by deleting the (AAAA) ip6 record. It explains why it stopped working through data plans and hotspots (which use ip6) but it doesn't explain why it was working for three months than stopped abruptly. It may just be a digital ocean issue integrating ip6.
Thank you all for your help.
@mehdi Digital Ocean. I gave the keys to the DNS to Cloudron. Also all the other DNS services we are using through digital ocean are working including communtiychest.io (Ghost) and akcu.org (XMPP) - this includes the other cloudron site on the same box (survey.americankulak.org).
@nebulon I sent and email to support@cloudron.io from president@americankulak.org with SSH root access and a Cloudron username and password login. I referenced this post and you. Thanks
@girish In terms of device we have noticed that it effects phones more. Also, we noticed that if it doesn't work on the phone through data, when we use a phone hotspot it hasn't worked on any device that uses that hotspot - so it seems to be a combination of connection method and device. So far the browser used has had no effect, if it doesn't work on one browser on a given device for a given connection it won't work on all the browsers for that device, although we have less examples of guys testing multiple browsers on different working devices.
Finally I noticed that the problem started almost exactly three months after we set up the americankulak.org domain on the box so it might be a problem with the Cloudron autorenewal for americankulak.org as the other site (which was set up weeks later) survey.americankulak.org is working fine. Although this doesn't explain why the admin page my.americankulak.org has always worked.
About three months ago we switched our website from a plain digital ocean Wordpress droplet to a Cloudron Wordpress droplet. Everything was working fine until it all the sudden some users started complaining they couldn't access the site on their devices - and we didn't mess with the website in between. Initially most the users had no problem but some depending on their device where either getting this error 
or this one:
Over time it started affecting more users and devices. It is even more strange because we have never used "Nextcloud".
