Edit: fixed in latest.
In my local board the following happens within the popular site:
There are 10 entries (all posts within the board visible at once, this may cause the trouble?).
If I scroll down the last 6 entries always repeat with infinite scrolling.
Can you give us your site url?
xD I haven't any hosted one, sorry...
I can add that I use MongoDB.
Here is a video of the bug occurring:
Update to https://github.com/designcreateplay/NodeBB/commit/ae93c372fffdb371f7a7eacd5d0aebc3b3ce6d12 and let me know if it fixes your problem.
@baris seems to work now