I'm pretty sure I logged this one already but I couldn't find the original bug report after searching a little bit.
Just encountered a fun variant of this one that might contain some clues.

Defensive (pre snap only?) penalties that should result in a 1st down for the offense don't. Instead the offense gets a play free of any down and yardage requirements.

7:50 3rd and 2 Buf - 37 Rush by Winston, J. for 1 yds. Tackle by Dabney, R.. BUF 20 - CHI 10

It's 4th and 1 for Chicago and they decide to go for it.

7:30 4th and 1 Buf - 36 Buffalo Penalty on Wilson, L.: Encroachment. BUF 20 - CHI 10

5 yard penalty from my Bulls should give Chicago a 1st down on the 31.

7:30 --- Buf - 31 48 yard FG by Pineiro, E. is NO good. BUF 20 - CHI 10

You can see that there is no down and yardage on the next play, but the yard line has been correctly adjusted.

What was fun here is that Chicago has changed their mind and are now kicking a FG even though it's not really a 4th down! The game must somehow think it is.

What usually happens in this situation is that the offense runs a play and then things start over with a 1st and 10 from wherever the "free" play ended.

Another interesting instance of this one, with an additional "clue" to what may be happening.

14:34 2nd and 9 LV - 40 Pass by Belt, S., complete to Jones, Z. for 6 yds. Tackle by Wheat, F.. LV 10 - BUF 17
14:05 3rd and 3 LV - 46 Buffalo Penalty on White, D.: Encroachment. LV 10 - BUF 17
14:05 --- Buf - 49 Play nullified by Las Vegas Penalty on Miller, K.: Holding. LV 10 - BUF 17
13:51 3rd and 8 LV - 41 Pass by Belt, S., complete to Agholor, N. for 7 yds. Tackle by Wheat, F.. LV 10 - BUF 17

On the 3rd and 3 play there was a defensive penalty that should have resulted in a 1st and 10.
The next play got run with no down and distance. Yardage was correctly moved up 5 yards.
On that play, there was an offensive holding penalty. The correct down and distance after that should have been 1st and 20.
It got listed as 3rd and 8 though.

Pretty weird. It's like it's treating it as a 5 yard penalty stemming off of the old 3rd and 3.

Ah, I get it now!

3rd and 3.
Encroachment penalty makes it 3rd and -2
Holding Penalty makes it 3rd and 8

The game is seeing the -2 and that leads the down and distance to not get displayed. But 3rd and -2 is what the game thinks it is and it moves from there.