„Connection to server lost“ in activity app

Nextcloud version (eg, 12.0.2): 13.0.0
Operating system and version (eg, Ubuntu 17.04): Ubuntu Server 17.10
Apache or nginx version (eg, Apache 2.4.25): Apache 2.4.29
PHP version (eg, 7.1): 7.1 fpm

The issue you are facing:
When activating mod_http2 in apache, there some issues with nexcloud. Activity app says „connection lost“ and same thing appears when trying to generate a share link.

Steps to replicate it:

  1. activate http2 in apache
  2. see the mentioned issues
  3. switch back to http 1.1 and everything is fine