About the only solution I'm aware of {yes, besides monkeying with the feed lips} is to make a shim of sorts with a material like a piece of polyethylene chopping block and rivet it to the follower.
Just exactly why some L-E mags are finicky and some not is sometimes hard to say, even comparing an "obedient" magazine with a "disobedient" magazine. I worked with many L-E's for many years and found some smooth feeding and some total buggers. Some fed when the bolt would be operated fast or slow 100% but not the other way around.
Recognise that for the most part many mags are pretty beat up these days. The magazine, while not being strictly speaking a "detachable" mag in the sense that it was issued as such {they weren't, tho originally intended to be issued in multiples to each soldier, once the charger was refined that device took the place of the "detachable" mag} they were nonetheless a weak link in the L-E system, with feed lips easily bent and dented, etc. So, many L-E's today have magazines that are totally out of spec even for the .303 cartridge. Fortunately they can be easily bent and adjusted...and equally easily messed up...
My recommendation would be to try it all, including buying more magazines. Try swapping parts, too, and shims as well.
As for the threads between the P14 and the No 4, they are totally different.
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