Interesting. It doesn't happen here although I almost missed it because it is positioned way down at the bottom of the page about 1.5" below the line of text.
I do have this template mod:
https://xenforo.com/community/threads/floating-navigation-bar.19295/
Could that have anything to do with it?
Unfortunately I have no idea when it started because I don't normally use Safari but had it open to do some troubleshooting of the Viglink add-on.
BTW, I'm using the default theme and these add-ons:
Add VigLink Code 1.0 (Disabled)
Amazon/Ebay Parser 1.2.6
Hotspots by Waindigo 1.1.1
Live Update 4.0.0
Newest Post First by Waindigo 1.0.4
Post Ratings 1.7.2
QuickSearch in Header 1.1.1
Register Email 3.1
s9e Media Pack 20150611
Show Deleted 2.1
SK Mark Thread as Thread 1.2.0
SV - Responsive Social Sharing Buttons Lite 1.3.4
Tapatalk 2.4.2
[bd] Widget Framework 2.6.0-dev
[ITD] Add Custom Icon and Link with Tool-tip in Footer. 1.3.0 (Disabled)