I've looked into this more and this isn't a bug. It's just a different display of the same information given the different UX goals of each page.

In notifications, we want to give you the information you might want to know about in a concise way. So we group "reward" notifications that are adjacent in the notification list into a single "reward" notification. So if you received rewards on Day 1 and then again on Day 2, and there were no other notifications between Day 1 rewards and Day 2 rewards, you'll only see one reward notification in your notifications which add Day 1 and Day 2 notifications together.

If you imagine you mostly tip on SN and don't post/comment, if we didn't group them like this, your notifications would be mostly a list of reward notifications (which stackers were annoyed by and called "spam").

In satistics, we want to give you all the information we have about changes to your money (and also when that change happened relative to other changes). We don't group anything. (I'll add the time it happened to this list because I know people want that.)

This is a case of grouping. Day 1 you received a "reward" for 692.548 sats. Day 2 you received a reward for 3.947 sats. You should see both in satistics and separate. You'll see them combined in your notifications.