I had the same too. Compared to November (as Dec bonus was boosted a bit IMO so i thought it won't be useful to compare) I wagered about the same & also the "bonus" amount from the statistic was about the same (actually a bit higher than last month) yet only received 1/3 of what I got in November.
When I saw the bonus amount today I literally said "must be kidding eh!?" Lol