Broken for me as per https://www.theregister.com/2021/01/12/flash_is_dead/
(chomium on linux, have been trying pepperflashplayer and/or SuperNova). Setting system clock back to yesterday's date as per reader comments works :)
Fissile, the scoreboard was resetting nightly for it bit. Don't know why. I saw the 50-pointer too. I'm happy I'll work back to my PB in due course, but I do have a screen grab (from February) that shows you at 47 lines...
IIX is right. The same thing happens with the 'S' and 'Z' blocks too, when they're horizontal (and you complete only one line).
What I can't work out is that because the intention is for the game to be hellish whether it's technically a bug or not ;)
 "Hell Tetris"){kind=icon}