So, I log into the site, and I click "Unread Posts."  Then three topics pop up.

I think "Huh.  I haven't tried this in 12 hours.  Seems unlikely that only three topics have been added to."  So I click the button a second time.  Twenty-three topics pop up.  I think "This is interesting.  I'll try it again for a few days."  And, consistently, over the course of several days, when I first visit the forum, I click "Unread Posts" and get a trickle.  I click it a second time, and get more hits.  How many more varies depending on how long I've been away, but it is consistently more hits.

Are you viewing the site on multiple devices? Each time you do, it counts each time as a "visit".

I notice that when I switch from Tapatalk on the phone and view the site on a web browser (or vice versa), it sets the posts as no longer being "unread" since the last "visit".

Not usually.  Usually it's the same computer across a day.

In fact, it just did it now, with my first visit of the day.  The initial click gave me a handful of new posts.  I type the above response to this one, then clicked it again, and got two screens full.

I am not completely sure, but I believe that if you click on the "unread posts" then it'll show that... post not read by any one.  If you click on "show all unread topics" on the "unread posts" screen then it'll show all the posts 'you' haven't read.... or something like that.      I dunno.. 

All I know is if I click unread posts, I get only a few.  I click show all unread, I get choke..  haahhaa

I don't have a "show all unread topics" link or button.  There is an "Unread Posts" button at the bottom left corner at all times, and on the index page, there's a larger "Unread Posts" in the blue banner.

When I click the little one at the bottom, I get more hits than when I click the large one at the top.

Screenshot attached.

I don't have a "show all unread topics" link or button.  There is an "Unread Posts" button at the bottom left corner at all times, and on the index page, there's a larger "Unread Posts" in the blue banner.

When I click the little one at the bottom, I get more hits than when I click the large one at the top.

Screenshot attached.

The one in the blue banner is just for that section. The one at the bottom of the site will give you all the unread posts for the whole site, or at least it should.  Are you clicking on the one in the banner then the one at the bottom? That would seem to explain the discrepancy.

The one in the blue banner is just for that section. The one at the bottom of the site will give you all the unread posts for the whole site, or at least it should.  Are you clicking on the one in the banner then the one at the bottom? That would seem to explain the discrepancy.

Yep. That explains it!