right now this is the view when i visit the official download-link of nextcloud:
→ it’s the same when i try to upgrade from nextcloud 11 with the upgrader in the web-interface. the step “downloading” fails with “certificate expired”
Same here:
download.nextcloud.com uses an invalid security certificate.
The certificate expired on 28 de julio de 2017, 19:01. The current time is 28 de julio de 2017, 20:39.
Error code: SEC_ERROR_EXPIRED_CERTIFICATE
Yes, I had the same problem. Had to cancel the upgrade unfortunately.
I have the same problem too.
Same problem. Can not download php install file. Can not upgrade. Can not perform clean install.
It’s fixed - certbot broke 
we’ll be looking for another solution 