I tried setting up a new !gnusocial instance on https://n4rky.me . But things seem really awful there. Subscriptions never complete. And I still see in the logs:

[Mon Sep 12 21:30:48.066537 2016] [:error] [pid 13163:tid 37174202368] [client 78.46.90.23:38945] PHP Notice: Undefined property: ActivityVerbPostPlugin::$notice in /var/www/new-gnu-social/gnu-social/lib/activityhandlerplugin.php on line 556
[Mon Sep 12 21:30:48.066565 2016] [:error] [pid 13163:tid 37174202368] [client 78.46.90.23:38945] PHP Notice: Trying to get property of non-object in /var/www/new-gnu-social/gnu-social/lib/activityhandlerplugin.php on line 556

Which suggests to me I haven't solved the problem by setting up a new instance.