I bought a cheap work light from Aliexpress and added the battery option, these turned up with it,
So I tested them both at 1A and one is very erratic during discharge,
Anyone ever seen anything like this before?
It may be bad line contact.
Any cell rated 4200mAH is bound to be Bad News™.
Whenever you get “included cells” with a light, it’s like ordering sushi from a gas station. Ie, not a good idea.
There are exceptions (Imalent, Sofirn, Thorfire, etc.), but generic Amazon/Fleabay/AX fare is generally not among them.
Give these to someone you hate, and get some decent cells from a reputable seller.
There are no 4200mAh cells. Therefore, highly suspect. Your results seem to indicate a poor cell, and a worse one, either with a poor contact or inability to sustain anything near a 1A draw, which should be easy for any 18650.
Hey look it’s a “Rechargrable” “Lithum” battery.
Only the finest quality I’m sure. 
As of July 2019, there are no 18650s with capacities over 3600mAh.
The best 18650...
Just lookit all those 5-star ratings…
it says high performance on the wrapper so it must be good.
I think I will probably bin them, especially as the really bad one obviously has some serious problems, don't want it going pop on me :)
Craptastic cells performing craptastically.
Who would have thunk it?
Don’t cheap out on anything ‘lithium-ion.’
Buy cheap toilet paper and lite beer if you have to save a few shekels.
Chris
Don’t listen to him!
I always liked cheap TP better’n the “fluffy” kinds, true.
But NEVER EVER settle for cheap b33r. It’s swill.
I'm the opposite.
When I drank beer, I got the very cheapest.
I think it was Keystone Light.
It didn't taste like beer, which is why I liked it.
And TP...
I like Aldi's version of Charmin Extra Soft.
It's somewhat reasonable price-wise, though there are plenty that is cheaper.
I’d dare say most mainstream domestic b33r doesn’t taste like b33r. Soapy-tasting beer-smelling seltzer, to me.
I could make do with gas-station TP, ’though. Single-ply Scott’s is fine.
My family loves single-ply Scott.
I think it's the very cheapest out there, and we're (generally) a thrifty bunch.
Oh, nothing unusual going on here…when people talk about crappy items, the topic usually ends up to the toilet… 
Yep, perfectly on-topic. 