You can try to snug up the thumb hole a pinch with tape in different spots.You can also go a little more forward in the thumb pitch if your not a fan of tape in the thumb slug

Get up to the foul line instead of 6 inches behind it and you will get the ball further over the line.

You'd be better off spending time trying to get your hand into a stronger position than spending time trying to keeping your hand in the ball longer.

I had the same issue as you describe a few yrs ago. I was losing my feel on the downswing of my approach .My pitches then were 1/8" reverse  x  0" lateral. I change my pitches to 1/8" forward x  1/8" left and that fixed the problem immediately. I've always had my thumbs pretty tight in the slugs to help loosen up my swing.Ive also had good luck with a 1/2" piece of white tape on the outside of my thumb slug to create a little drag sometimes, for a better feel

You can try to snug up the thumb hole a pinch with tape in different spots.You can also go a little more forward in the thumb pitch if your not a fan of tape in the thumb slug

xray, I would try a piece of Hada patch blue tape on the back of your thumb to tighten up the grip just a bit.

I looked at your video---good form. Your thumb was clearly out of the hole as your hand was passing your sliding foot. For what little it may be worth, here is what I try to do: accelerate my arm swing at the bottom of the arc as my right hand is reaching my sliding foot. I have no video of my approach and arm swing, but I am pretty sure that my thumb exits the ball as my hand is at the toes of my sliding foot as you indicated.

I could not make that acceleration at the bottom of my swing if my thumb hole were even slightly loose. I usually add a piece of Hada patch blue to the back of my thumb after a couple of practice shots. My thumb grip is fairly snug, but I can still feel a bit of "wiggle room" after several shots. You may think that your grip is snug, but I am guessing that you may have just enough looseness to cause your thumb to slip out early.

Try the Hada patch blue. Good luck.

Never heard so much BS in my life.  Just tuck up the fingers and push the ball out onto the lanes.   If you can't hold up the ball with your fingers you're just wishing you could bowl.   All this BS about holding onto the ball with the thumb is just that, BS. 
Thank you    Bullred

I use MC and white tape with 1/8 forward and 1/8 left. I already have a snug thumb, but I guess it can go a piece more, i just have to see. I lost more weight from this video and the thumb hole is slightly looser now.

My early turn is something I've been dealing with for awhile now. I've done drills, have mental thoughts, etc...but my body just doesn't cooperate, but I'll continue to work on it.

Jay,

I like a really tight thumb because it allows me to relax on the downswing and just let the ball be pulled off my thumb by the weight/momentum of the ball. However, if I find the thumb hole is too tight, what often happens to me is I relax so much to allow the ball to be pulled off that it falls off early. For all intents and purposes I drop it.

Unless you're cupping the ball such that your thumb is under the ball (as bullred, in his infinite wisdom implies, without explanation), there is a proportion of thumb pressure and relaxation of the thumb that you need to control.  If the thumb is so tight that you need almost no pressure to hold it, it's hard to know when to relax all pressure, in order to allow the ball's momentum to pull itself off your thumb.

Hada tape will roll up or come off if one knuckles his/her release.  I see many that have poor fit that use Hada tape that have to replace it.  It's the ones with poor fit that tend to knuckle or don't use tape inside their thumb hole to get a tighter thumb hole that have issues with Hada tape.  Straight thumb, tight thumb hole, no knuckling, no issues.