6292aa5 added a check to `\OCP\IURLGenerator::getAbsoluteURL($url)` whether `OC::$WEBROOT` is already prepended to `$url`. It does this kinda naively and is thus error prone.
So in case ownCloud is installed under `/oc`, `OC::$WEBROOT` will be `/oc`, then the URL generator checks `substr($url, 0, strlen(\OC::$WEBROOT)) === \OC::$WEBROOT`. Since `$url` is `/ocs/apps/notifications/` it will now compare `/oc` with `/oc` and won't append the webroot => 💣
Considering that this is rather a very error prone feature which is not used from a search over the core code I'd recommend to remove this logic.