I suddenly lost 50 points on SO, and since then have not gained rep despite a bunch of upvotes (still under the 200 rep cap).
Update: my daily rep earned was 247, then dropped to 197 and since then has not budged, despite upvotes.
Most probably you hit the rep cap with those 247 points, so that upvotes won't count anymore for the day.
Then one of the questions that you answered, and for which you gained 50 points, got deleted.
Now the "recent" rep tab only shows the still existing upvotes, but new ones still don't count since you already hit the cap today.