STUCK in HANDPHONE, SAFARI Browser

I have no issues so far with EASY TOC on my WP website…

However, a few of my users, over past weeks have complained of persistent bug.

This is noticed when they open any link sent to them, especially blog posts, on their mobile phone.
Some use iPhone, thus default is Safari Browser.
When they go the link, still no issues.
Then, they start scrolling down to browse and read.
They will reach the Easy TOC Table of Contents…
Still no issues.
Then, sometimes they may click on a particular content/link on the Easy TOC (main post, not sidebar or widget).
The link will scroll them down to the specific anchor URL. Still no issues.
(Update: I noticed a small issue here. By default, I use offset function to account for the sticky header I have. I noticed that, when using mobile Safari, the offset is not seen to be in effect too, and this is linked to the problem of being stuck – read on below.)
They continue reading.
THEN, the PROBLEM ARISES.

They cannot scroll up or down. The viewport is basically stuck permanently at wherever the Easy TOC link/href has brought them to. The issues is only resolved on F5/refresh entire webpage.
(Update: I noticed that after refresh, now the offset is in effect, and there is no further problem of being stuck. However, why does the initial PROBLEM of ?no offset + ?stuck on easy TOC anchor link occur??)

Appreciate any help pls!

The page I need help with: [log in to see the link]