Ender 3 prints mostly ok but suddenly stops extruding

@clh  Maybe check the screw that is holding the extruder lever is not too tight. When thicker piece of filament is passing the spring can't push it back to tension because lever binds.

Check the extruder tension lever, you will need to remove it, they have a bad habit of breaking, as they fail you get the mentioned intermittent fault.

I am having this issue as well. The print starts great and gets about 20% into the print and then jams. i have a new alloy extruder and upgraded hot end and new nozzle.

The extruder seems like it's working great, when it jams, you can see that it's starting to compress the filament as it gets harder to push, then it's literally grinding the filament down as everything jams up and stops.

it's almost as if the end loses temperature but it appears to read accurate on screen. Very confused.

I agree with the other commenters, it sounds like there's something wrong with the extruder.
Most likely the arm is cracked, which you can't see from above. Also, the grub screw holding the extruder gear on the motor may be loose.
I'd really suggest replacing with an all metal extruder. Sooner or later you'll need to do it anway.

I've had the problem with my ender 5 pro. I solved it by changing the retraction to 3mm. The defaults on the creality slicer seems to be 5mm. At 5mm retraction tends to block my hot end and stops further filament flow. You may get some stringing but its not bad. Also, before printing, I tend to heat the extruder and once heated, move the extruder, say 10mm, and make sure that the filament is extruded properly.

OP here.  Turns out it was the filament.  I got a roll of Hatchbox, installed that, and it's been perfect prints since.  No failures at all.  So I don't know what's wrong with the original filament but I'll never buy "JAREES" brand again.

For additional details on what I tried before that...

I had posted in a few places about this and I got a reply on Reddit that seemed to point to heat creep, so I looked at everything tied to that too, but nothing helped.

My printer is brand new, had it 2 weeks so far, and it never printed correctly with that old filament out of the box.  So it was unlikely that something like the extruder arm would be cracked on a brand new unit.

That said, I take the extruder arm off and verify that it wasn't cracked.  I made sure the screw on the arm wasn't too tight.  I tried both tightening and loosening the spring tension on the extruder arm. (Tighter made it worse, of course too loose and it wouldn't push at all.)

One other thing I noticed after posting the original question was that when it had issues the extruder wheel would "skip".  I could even hear it when it skipped.  This is one of the things that led the person on Reddit to believe it might be heat creep.

I even took the hot end apart and put it back together to make sure there wasn't a clog and that I had a good seal on the PTFE tube.

I got the same problems with my printer. Ender 3v2 and CR-10S， Cleaned the hot end, including brass nozzle, throat, and PTFE tube for Ender3v2. I did not find anything clogged but after finishing the cleaning, it works well again. 

Unfortunately, when I do the same thing for CR-10S，I broke the thermal wire....

Updated: figured out what's happening. could be a problem I've heard of called "heat creep" into the heat break. I have a new titanium one so I thought it would be better. when I dismantle and clean up, there is always a 'plug' in there - the jam I assume (see pic). 

I started printing with no retraction and it completes now. Stringy of course.

There was someone who said that the amount of retraction is changeable but I can't seem to find it in the menus.