Thank you @Mario Vavti My report was incomplete - and I found the bug in the logs. Superblock was enabled, disabling it stopped the error. Uh. That must have been me causing this, as i was using some code from superblock for a new addon (which was disabled before). My new addon works, superblock doesn't. I guess i am not built for such things, however trying this to get features i am missing, that's why the dev site.

Stack trace for the record
#0 /home/site/devsite.net/include/plugin.php(504): superblock_enotify_format()
#1 /home/site/devsite.net/Zotlabs/Lib/Enotify.php(895): call_hooks()
#2 /home/site/devsite.net/Zotlabs/Module/Sse_bs.php(215): Zotlabs\Lib\Enotify::format()
#3 /home/site/devsite.net/Zotlabs/Module/Sse_bs.php(99): Zotlabs\Module\Sse_bs->bs_network()
#4 /home/site/devsite.net/Zotlabs/Web/Router.php(223): Zotlabs\Module\Sse_bs->init()
#5 /home/site/devsite.net/Zotlabs/Web/WebServer.php(110): Zotlabs\Web\Router->Dispatch()
#6 /home/site/devsite.net/index.php(14): Zotlabs\Web\WebServer->run()
#7 {main}
thrown in /home/site/devsite.net/extend/addon/hzaddons/superblock/superblock.php on line 193

note there is no domain devsite.net...