After upgrading to PHP7, Nextcloud returns a blank white page

Nextcloud version: 12.0.1
Operating system and version: Debian Stretch
Apache or nginx version: Apache 2.4.25
PHP version: Previously 5.6, trying to upgrade to PHP7
Is this the first time you’ve seen this error?: Yes.

Can you reliably replicate it? (If so, please outline steps):
Yes, I have restored from a backup and attempted the upgrade process a second time with the same result.

The issue you are facing: When I disable the Apache php5 module and enable the php7.0 module the result is a blank page when trying to visit my Nextcloud server’s URL. Disabling PHP7 and re-enabling PHP5 returns the Nextcloud homepage as expected.

You might didn’t install php7 modules.

Show us your apache log, there will be lines saying something missing.