Hey bud, I'd like to say hi and welcome to Vaping Underground
I haven't used factory made OCC nickel coils yet but I can tell you with some of my atties my DNA40 mods can read as much as .02 off from what the resistance is supposed to be of my nickel builds and .02 in the nickel world is like .2 in the Kanthal world in difference of resistance and when you're talking in terms of temp control that .02 can make or break a vape turning it from all that to complete crap instantly. Just something to keep in mind as you think about getting into building with nickel....make sure you clean your wire with alcohol as well and do not torch nickel like you would Kanthal...it will change how it behaves and winds and reads the first time...you want the wire as clean and unadulterated as possible the first time you screw it on your mod and fire it.
However I can tell you that the Stock Nickel coils are supposed to be .15 ohms so I am assuming your .5 ohm coils are the standard ones and not nickel correct?
What wattage setting are you using your .5 ohm coils at? The temp setting doesn't matter with Kanthal and Nicrome builds because the mod can sense it's not a nickel or Ti build and will put you into straight power wattage mode. The stock .5 ohm OCC Kanthal coils don't really like to vape above 25 watts, especially with thicker liquids. Kanger has come out with some new .5 ohm Vertical coil heads with even larger juice ports that is supposed to solve this problem but with any stock coil made by anyone throughout vaping history they always seem to exagerate what their coils can fire at. For just a fictional example....lets say Clearo Style A has a 1 ohm coil that says it can fire from 5-20 watts....in reality it can only work in about 7-15 watts and will suck below that power band and burn and taste horrible above it...it's the same with the OCC standard coils.
The .5 ohm doesn't really like to go above 25 watts without playing with the wick to get it to suck up the juice faster and the 1.2 ohm coil I had didn't seem to like to go above 18 watts and my friend's mother I got vaping ....well, he bought her a subtank because he's an idiot so I got her a bunch of 1.2 ohm coils and modified the wicking and she runs them at about 12 watts and she loves them even though it's a bit much vapor otherwise.
In regards to your nickel coils, like I said, a .02 difference can really impact the vape quality...they're supposed to be .15 so if they aren't .14-.16 then they're going to vape differently, or your mod can be reading the resistance wrong like one of mine does and you have to trick it into reading the right resistance and how to do that is a little different with every chipset and I don't have an invader mini so I couldn't tell you for sure if my trick would work right for you.
As for if anyone has gotten a bad batch of coils? I am sure someone will come along and see this and chime in about that...the thing about these coils is they are mass produced in the hundreds of thousands if not higher and a few bad ones will always slip threw since QC on something like this is quite impossible to be perfect without firing every single coil....Kanger's dual coil setup for the aerotanks and protank 3's and genitanks are complete garbage, I got intire 5 packs of replacement heads and I had to rebuild all of them because they were all complete crap...if it weren't for the Subtank being as good as it is I believe that the vape giant would have sunk...they really pulled their asses out of the fire by getting this one right.
One thing you can try and do as well is taking a needle and fluffing out the center of the wick and poking holes all the way threw the center to the coil to kind of help guide the liquid where it needs to go...it helped me...I only run my .5 ohm coils at about 24.5 watts and it seems to be hot enough for me and solved the dry hit problems I was having.
And like I said, someone will see this and come along and chime in and probably have something more helpful to say but I hope this helped at least a little. Best of luck to you, get a couple more OCC coils and try the settings and fiddling with the wicks like I said and see if that helps before you dive into temp coils again....just get a single nickel coil if you can and see what it reads at....and let us know...it will give us a baseline to help you from..
best of luck to you and wishing you better and happier vaping soon