If it feeds sweet on semi.....
Then it is:

Magazine - not able to feed at higher speeds/spring not strong enough to feed bb's on auto or other possible feed issues like follower getting caught/binding at bends of a snakey mid cap spring
Check mag and/or try other mags - heck even a high cap wound up loads & loads
(too many people rip stuff apart when in fact it can be mag related)

Delay clip - even if one is installed - some are better than others and fitted better than others - might not just be a matter of holding tappet/back longer duration but also ensuring that tappet plate retracts as much as possible
Tappet plate is probably not worn but what I mean you can hold the tappet/nozzle back as long as you like but if nozzle struggles to clear the hop's feed tube then you will always have feed issues especially on auto

Double firing rarely takes place but is a result of misfeeding...

The gun fires but where it fails to fire the bb say, this "might" be down to tight bucking lips that restrict the feeding, stays in hop/barrel then a second bb finally manages to load & when fires you get two bb's exiting and a drop in fps due to 2 bb's

eg: 1 - 1 - 0 - 2 -1 - 1 - 0 - 2 - 1 etc....

you can still get a misfeed and no double eg: 1 - 1 - 0 - 1 - 1.......

check you can manually feed a bb through hop unit & the bucking lips with a mild bit of force - tight bucking lips will result in feeding issues

see timeline 3:00 aprox for the bucking lip test
(do not think you need to mod or do other stuff in the vid, yes watch it all but linked it to show the bucking lip test mainly)

I doubt if the hop/box/nozzle is misaligned (possible but tbh I doubt it)
most likely it will be a mag or hop problem I would expect
but not got it in front of me so am taking a few possible stabs at stuff to investigate further

hope some of this helps

 

Sadly it only feeds sweet on semi when you spam the trigger, fast firing.
I have another hop unit in an other rifle I might swap over and see if that's the issue. tried lots of difffernt mags and all the same

 

Sadly it only feeds sweet on semi when you spam the trigger, fast firing.
I have another hop unit in an other rifle I might swap over and see if that's the issue. tried lots of difffernt mags and all the same

Well that is a bit odd semi is semi to me - even spamming on semi is not allowing the gun to spin/feed so fast like on auto

anyway - now try another hop unit/barrel setup if possible
some hop units can be a little different to others
some people have trouble with a pro-win unit & others run perfectly fine

The nozzle could be smidge too long but I'd avoid the urge to file it down as if it doesn't seal you lose fps

what you could try is a small thin o-ring in between the hop unit & front of box first - this will push the hop unit forward a tiny bit
you may be able to track down a small thin shim in say 0.2mm thick & 11mm inner diameter as a more permanent fix/bodge

Try to shift the hop unit forward a small tiny bit that will hopefully have the effect of the nozzle clearing the feed tube better and chamber bb after bb more but hopefully not lose too much fps in the process

sounds like nozzle not clearing just enough, maybe a shorter nozzle or filing of nozzle carefully but then shave front of tappet plate to push the nozzle further to make up for it all - ergh if you understand

there are mods & different delay clips to extend the tappet plate travel as well as the duration the tappet plate is retracted but often it is the travel length not duration it is held back for that helps with feeding....

As said you can hold the tappet back for yonks but if nozzle is struggling to clear feed tube then you will still suffer poor feeding

Eg: DSG's chamber bb's at 40 - 50 - 60+ rps but they do not have delay clips and a shortened tappet fin as well, can't use the normal delay clips or tappet won't return in time to chamber bb properly so the delay clip isn't always the answer if you can increase the tappet plate's travel length

Try another hop unit - the bucking lips might be catching if showing in feed tube - no I do not advise grinding stuff unless you are sure it is the hop unit itself and are getting desperate and give a damn in the end....
try another hop unit/bucking - some lips protrude more and are tighter in some hops than others - it should all work but alas it often doesn't all go as planned
Try to shim or push hop forward just a whisker to help nozzle clear & chamber but watch for fps drop

Other wise the nozzle/tappet/delay may need investigating if all else fails