up arrow not displaying on all pages on iphone

I have another ios11.3 issue. The scroll up arrow that shows up on bottom right as you scroll down a page (a real handy feature), only displays on the front page of website on i0s11.3. On laptop and android it shows up on all pages. I suspected another plugin conflict, so I did disable all plugins except Jetpack, but it still only displays on the front page, and no other pages. Any ideas? Thanks.