I was awestruck looking at my activity monitor, there was tons of Filemaker Web Content, and Filemaker Network sub-processes. Like in this screen shot.
It turns out that each time a webviewer is refreshed, a new couple of web content + Networking process is launched, but Filemaker 16 /17 forgets about them, and don't kill them when the same web viewer is refreshed.
On my layout there's only 1 web-viewer, that gets refreshed to a new content, it's not multiple webviewers.
I've a video of this, but doesn't want to share publicly (confidential stuff)