I have a Phantom 3 standard with an ARgtek range extender. (i also own a DJI MAvic)
Is it me or does the Phantom 3 standard just have days where it doesn't want to behave?

For example, I done a small recording job for a freind over a open football pitch at 3 pm. no more than 200meters in distance was flown and a max height of 50meters. drone was LOS the whole time, with nothing in the way to stop connection.The drone performed perfectly.

I then came back to the same place at 8.30pm to do some night shots with the flood lights on, exactly the same flight plan as performed @ 3pm but the drone just wasnt having none of it.
First the live video link screen went black and white and froze like it had lost connection, even though there were no warnings about connection when the drone was only 20meters away. I landed the drone and restarted everything, i took back off and the drone just wouldnt hold steady at all, trying to fly in a straight line was near impossible, it was drifting pretty hard left. so I landed again and restarted everything. Then once in the air again the max distance was approx 75meters before the signal was lost and it intiated RTH. I gave up and took out the MAvic.

Take the P3S back this morning and again its performing perfectly. No connection issues, nothing.

This isnt the first time this has happened where the drone just seems to misbehave, Its like one day its perfect, next its a little $hi%...

Does anyone else suffer the same ?
and Is there anything better than the Argtek range extender out there that is really worth buying?

I recommend ITELITE (dbsmods) over argtek.  

Are you sure you did the mod correctly?  No loose or broken connections?  No crimped or pinched cables?  Are you sure you're aiming correctly?