Ok, I've been looking into this a bit. The default expiry date for the phpbb cookie that gets created when you check "Keep Me Logged In" or whatever is 1 year. Unless this has been changed it should still be set that way.
When you're on one of the forum pages, right click it and choose "Inspect Element". Expand the side panel a little, and choose the "Resources" tab at the top. Navigate down to "Cookies" and expand the tree view. Should see a nested "www.pedrothelion.org" value there. Click it and expand the panel further so you can read the columns. There's a column called "Expires / Max-Age" - what's the largest value of this column for the four rows there, i.e., what is the date value that is farthest in the future (ignoring "Session")?
If you want to get your hands a little dirty, PM me and I'll show you how to go through the Chrome Cookie database with SQLite and we can compare data, which may be useful.
If all of that is normal...are you posting from home or from work when this happens? If it's at work does this happen on other sites? Any chance they're refreshing cookie data in the browsers every so often?
when I was a boy
everything was right