I play on PC and I can confirm that quitting and not saving your progress midway through the Reaper’s Rewards Event causes the Reward Event UI to become blank when you re-enter the game, so I would recommend avoid doing that!
I had been reading the bug reports about the event, so to be safe before I even started it I turned off mods and started a brand new clean save with a new sim and the whole event was working beautifully; I got my points and was buying the rewards. Then the Welcome Wagon came over and Travis Scott read then stole my copy of Gardening Volume One. I didn’t want to waste my simoleons on buying a new copy so just quit without saving, my last save being before I’d spoken to 3 sims about Ambrosia. But when I loaded back into the save file the Rewards Event UI was blank and I couldn’t continue.
I tried Crinrict’s method shown near the start of this thread (moving the accountDataDB.package to the desktop) and this worked for me. I started a brand new save after following his instructions to the letter and the Reward Event UI was repopulated, yay! I was able to complete all of this week's tasks successfully, get all the rewards and re-add my Happy Home Login rewards afterwards.