Stuck drilling wood frame between floors

Question

Wiring 10 y.o. house with Ethernet. Read this; picked a spot; drilling 1st hole through the floor:

This illustrates exactly what I'm trying to do, so only flex-bit (no spade or auger) would work:

Started with cordless drill, but soon after changed to corded one. @ ~1.5" depth the flex-bit got stuck and the shank stripped. I thought of filing off 3 flats to allow for tighter grip, validating that idea found this question. Confirmed: it worked!

I clean sawdust inside the wall with vacuum (via a tube) and monitor progress with a borescope:

This looks like a subfloor OSB panel:

Notice the difference with previous photo - now I'm in solid wood:

I got ~3" down, but suddenly now the bit doesn't seem to bite anymore - just burns the wood, I don't understand why. Tried long enough, varying pressure - but no go; the bit comes out with charred gunk. Cleaned it several times:

Friction creates smoke:

The bottom of the hole now looks burned:

@Harper says "Hitting something super-hard means don't drill there" answering this question.
There are no noises of any kind. I'd expect some screeching or squealing if the bit was hitting a metal plate..

Picked spot lines up with between-the-studs cavity downstairs, which already houses TV cable (and thus has an outlet!) - I want to build up on that. Any advice?

UPDATE 2021-Mar-25
The flex-bit is new, I'd be very surprised if it goes dull after drilling only 3 inches :o).
As suggested, I tried it on a piece of wood, looks good to me:

Will try drilling a new hole to the right of the first one - through the same drywall opening. Would like to avoid messing with drywall: never done that before, and even if easy it involves painting => color matching..

Answer 1

You could have hit a knot in the wood.

These screw tip bits might not be able to pull through without additional force, which you cannot apply with a flex bit. Try a different drill spot from the same entry point, 3 to 4in over sideways. If it were a nail or a plate you'd hit hard and possibly jam, but likely not heat-up.

I did a similar hole with a straight auger/spade: with the box low enough and a long enough bit you can hit the right angle. Remember, you can cut a hole the size of the ethernet cover (minus a margin). But maybe it's too late for that since you have one entry point and don't wish to patch the drywall.

Also, from one DIY to another I'd add: don't be afraid for patch drywall work. Start with a 4in hole saw, and keep the cut out. Lots of videos, and lots of help here.

Answer 2

Well, I did get through! So I should probably write it down for anybody in the same shoes..
Having a borescope helped tremendously (both for drilling and pulling cables later)!

Cleaned up bottom of the hole, scraping it with a piece of strong steel wire and sucked debris with vacuum. Saw the opening in the middle and probed it - wire went in easily and didn't encounter anything:

Great - there must be an opening underneath! So continued to drill - carefully, controlling speed - not allowing to spin up to full RPM, getting stuck a few times, then reversing direction - releasing the bit, and switching forward again. Eventually it went through; I caught the drill not letting it go down and hit smth:

After successfully going through several more plates with very similar experience (i.e. stopping burrowing), my explanation is this:
The bit is primarily being pulled through the wood by the tip screw. Angle of attack on the main 2 cutting edges is too small to bite wood on its own, once that screw goes out. It wouldn't hurt to have sharper attack angle and .. better steel (as the bit dulls quickly, and can be filed easily).

Found a water pipe right under, so had to move aside within the same stud cavity and drill another hole. The bit doesn't really bend below the 1st plate. You have to position it so that it will go through both plates not touching drywall.. Used the 1st hole to observe - I can't imagine doing this blindly!

Bit's tail (left-top corner) hits opposite drywall if going with original inclination and starting point:

Positioned the bit more vertical by lowering and lengthening drywall opening:

Compare with 2nd picture in the Q - the bit won't bend that much (if at all) in an open hole:

And voila - 2nd plate is drilled!

Checked with a flashlight .. I'm lucky: no firestops. Done!

Drilling through another floor was a lot easier - I learned all the lessons :).
And yes, patching drywall pales in comparison, though I still tried to minimize the damage.
I'll accept @P2000's answer: he had all the right things spelled out (even if I didn't realize at the time).

So, yes, be careful, but patient. Persistence is not futile! Thank you guys for encouraging me!