I noticed this 2 days ago too. I gained 45 reputation before anything appeared in my reputation tab for "today" and then it happened again today. I just gained my first 10 reputation for the day, and I see nothing listed for "today" (it starts at yesterday).
This is a screenshot I took 2 days ago after my initial 25 reputation gain. I gained 20 more reputation after that and still nothing was listed. It all finally showed up ~15 minutes later. This is similar to today. The tab said 10 reputation (for change). I clicked it, nothing shows up for today. Now about 15 minutes later (again), it's showing up.
Is there some sort of new delay for results appearing in the reputation tab at the start of your day? Did this information get cached? I don't remember it ever doing this before, and additional reputation changes throughout the day always appear immediately (once the "today" section actually shows up).