oC 9.1.4 - failed to request notifications?

Having upgraded to 9.1.4, I now often see a message "Failed to request notificatios. Please try to refresh the page manually" at the top of the page when logged into oC.

Steps to reproduce
1. Log into oC 9.1.4 admin page
2. Wait a bit, then switch to the 'Activity' app
--> a yellow notification badge will appear with the message

Failed to request notificatios. Please try to refresh the page manually

Expected behaviour
No error message?

Actual behaviour
Yellow message is shown: "Failed to request notificatios. Please try to refresh the page manually"

Server configuration
(hosted webspace)
Operating system: Linux
Web server: Apache
Database: Sqlite
PHP version: 5.6
ownCloud version (see ownCloud admin page): 9.1.4
Updated from an older ownCloud or fresh install: updated
Special configuration (external storage, external authentication, reverse proxy, server-side-encryption): none

ownCloud log (data/owncloud.log)
3x the line

{"reqId":"XXX","remoteAddr":"111.222.11.222","app":"PHP","message":"Automatically populating $HTTP_RAW_POST_DATA is deprecated and will be removed in a future version. To avoid this warning set 'always_populate_raw_post_data' to '-1' in php.ini and use the php:\/\/input stream instead. at Unknown#0","level":3,"time":"2017-03-20T11:12:09+00:00","method":"POST","url":"\/oc\/index.php\/apps\/calendar\/v1\/config","user":"xxx"}

Integrity status for oC9+

No errors have been found.

Any ideas what is causing this and how to fix it?

Thank you

See the existing bugreport: