I've noticed with the S7E compared to my Note7, the S7E is a little more finicky with quick charging. Just yesterday, I had it connected to my old Note5 charger because I didn't take my new one out of the box, it said fast charging, but started at 39%,went DOWN to 38% a few minutes later, then only to about 42% after like 15 minutes. I plugged in my S7E charger and it went to like 78% in less than 30 minutes after that.
Maybe it has tighter tolerances in regards to when the fast charging actually activates or detecting an issue with the cable.
My suggestion is always try disconnecting the USB cable from the charging block and reinserting and maybe trying another outlet.