I am contributing after being cut off for a while, and just discovered that some tags like <activityfeed /> and <wikiaforum /> are not functional anymore.
It seems that ''forums'' are migrated to ''discussions'' and a new tag named <discussions /> is available (ref: Help:Discussions activity feed) — so I tried it, yet it doesn't seem to render anything on the actual page.
I left a sample reproducing the issue on a personal sandbox page for those who might be interested:
Can I ask for an explanation of what has happened to them, before filing an issue to the staff? Thank you.