$template->set_filenamescall within the (for example)
core.modify_notification_messageevent to appeng the message nicely
/cachefolder and its subfolders permissions? Also, are you using OPcache along with PHP7 (and/or other server-side caching probably)?
Yes. F.e. open Youtube video page in browser (paused), set the time slider at 9.00 mins, then click "Share" below and check the "Start at:" checkbox in the window opened. The link generated will get
t=9mparameter (without seconds).