You could try opening Chrome's devtools with F12, I don't have much knowledge to debug general issues from there but maybe you do, or you'll see something.
The 'Applications' tab shows, among other things, the cookies (after selecting "cookies" on the left, you may want to type "rpgwatch" in the filter if you have cookies from secondary sites).
- I did a quick test, taking a screenshot of the sorted cookies when the session was fine, then messing with one of them, reloading and comparing the cookies.
It didn't tell much, but I saw the missing cookies which may be an indication. There's a "only show cookies with an issue" at the top, but that didn't show me anything. Perhaps you'll have more indications from all that.
- When I checked the open issues (see top right), I had two: one about quirks mode because of the header, and another irrelevant one about audit usage.
If you have an issue at this point, it's likely due to an add-on or to the settings like some restrictions on the cookies ("Sites that never use cookies") or another site setting.