There are at least two reports in ruwiki that the table of contents' hidden state isn't kept after page reload (I confirm). This could be connected to T195053. This is not wiki-dependent, not user-dependent, and it doesn't look like it's browser-dependent (in Firefox, the state is kept only when you press "Refresh", and that's probably some browser feature).
Steps to reproduce:
- Open any wiki page with more than 3 sections, for example https://en.wikipedia.org/wiki/Phabricator.
- Click [hide] in TOC.
- Refresh the page (in Firefox, click in the address bar and press "Enter").
TOC is hidden.
TOC is shown.