My ratio of quarterly dividends for VTSAX this year were
24.54% 24.76% 23.47% 27.23%
Last year they were
26.70% 18.92% 24.22% 30.17%
So I'm showing VTSAX 4Q divs down slightly from last years 4Q, but not nearly as much as you are showing. I expected some cuts in dividends due to the pandemic and big drop earlier this year. Over the whole year I show divs down about 5%, but given the growth in VTSAX the yield drop is bigger.
I've never seen a second round of dividends in a quarter for VTSAX. Did you sell any shares?
I've had my 1099-DIV come up short in the year I switched my VG account to brokerage, but that's because I got a second 1099-DIV that year--separate 1099s for the two account types. But you're not talking 1099-DIVs because those obviously aren't out.