Odds of this

played triple double bonus single line, hit four aces two times in 20 hands, no kicker unfortunately at .50 but paid $400 each time.  

Grok:

The odds of this happening are approximately 1 to 15,435,030 (i.e., the probability divided by 1 minus the probability, expressed as a ratio). This is extraordinarily rare—about as likely as winning the Powerball jackpot twice in a row (roughly 1 in 292 million squared, or 1 in 85 quadrillion, but still, your scenario is a cosmic longshot).

If I were playing, I wouldn't calculate the odds of hitting them in 20 hands. I look at it as, on average, you'll hit a 4-of-a-kind Aces in about every 5,760 hands, and I play 6,000 to 8,000 hands a month. What if I don't hit any more aces for the entire month? Now, I'm just above average. If I go another month without hitting any, I'm below average.

Two weeks ago, on DDB, I hit 8 4OAK in 2,056 hands; on average, I should have hit 5 4OAK. Last week, I hit 1 4OAK in 839 hands; I should have hit 2. 

It all works out over time, I hope! I'm still 2 short of Royal Flushes, on average, over the last 2.5 years. Watching the Bob Dancer interview on LVA, I liked the way he phrased it. He said, "I've been over Royal'd at times and I've been under Royal'd at times."

Just a different mindset on how you look at it.

I just have to say, I dip into TDB now and then, can't bear to stay for long 'cause it never hits much at all for me.  One time got kickers with an Ace, but that is one time in years.  Congrats on your Four Aces times 2!!

Candy

That's a good way to look at it.  I'm on a good run, hit four aces with a kicker 2 times in 3 days of play, then had a small losing session, no play for 2 weeks, then these four aces with no kicker twice in this session.  No royals, but I'm not complaining!

Yeah, it is high variance for sure!  Probably a bad game to play.  I tend to play it if I have just an hour or two, and I generally quit if I hit any quads or double up.

You need to factor in the number of hands you played. The odds of hitting four aces once in 20 hands are 20/5760, so the odds of hitting them twice are (20x19)/(5760x5760). Not quite as unlikely as you calculated: about a million to one against. Right up there with Adam Sandler winning the Oscar for Best Actor.

To clarify, my back of the envelope calculation was to answer, 'If you play 20 hands, what are the odds against getting quad Aces twice?"' I calculated it as a parlay: what are the odds of two things happening: you get AAAA once, and then you get AAAA somewhere in the other 19 hands as well.