After 250 rolls, 1 popped up 27 times. Or roughly 11% of the time.
I did this same test with all 17 D20's I have and 2 D20's from people in my DnD group.
This one was far and away the worst though I had more than I'd like with averages under 10.
Edit:
Here's the stats for the ones I tested
This excludes the data for the 2 D20's from the people in my DnD group as they didn't want that data shared outside of the group chat.
Very interesting statistical data set you have there, I'd be interested in replicating the outliers (particularly that 27 1's die) and if it isn't poorly shapen, don't reveal the follow-up stats and force the "cursed die" onto special rolls/annoying people in the party. If it is poorly shaped get rid of it imo,