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.
Looks like a bubble issue. Did you do the salt water test as well?
Haven’t done the salt water test mostly because I just wanted to see results before I did a test like that