If I read the latest FAQs correctly, a workflow task calling a webservice via HTTP will fail if called so after November 1st 2018.
If I am right it means one has to change the call asap to be on the safe side.
But, being on the safe side will not mean to be immune to such behavior as some old task with HTTP call might still be active. As some workflow task can last for quite some long time (for an order pending for instance)
Any recommendation to avoid problem ?