A small take from my side:
There have been rumors, personal beliefs and allegations against the G36 for several years now of being unreliable with it's accuracy. And it was perhaps the first mistake to not decisively verify one way or the other. It always lingered around. Perhpas sometimes with a small notion that unaccurate shooting was inteded to be blamed on the rifle.
After those accusations got worse a few years ago and indications seemed to support them, there was a proper test that found one specific type of ammunition to be faulty to the extend of causing the inaccuracy.
However, the problems, even with other ammo types, seemed not to go away, so there was another comprehensive test ordered. While AFAIK the final results are not out yet, the preliminary findings, wich have now been announed a week ago by the MoD, apparently show an actual, significant problem of accuracy with the rifles themselves. I think in a press conference I have heared the statement that rifles of all types (generations?) are affected. It was also reported that comparable rifle designs were much less affected, whatever that means.
So far the state of affairs is the weapon is safe to use. There's no specific danger of misfire of mechanical failure. It's just that under stressfull climatic conditions (hot temperatures, intense use and temp variations like direct sunshine / shadow) the accuracy seems to suffer.
As I said, the final results are still not there, so final conclusions will have to wait.
This could, however, have significant implications if the design should indeed be deemed unfit for duty use.
When the rifle was ordered and designed (the early '90s), we wanted a light, easy to use gun for central europe. Now light, to a certain extent, of course means less resistance to thermal stress. The temps here are lower then in AFG or Mali, and I think people didn't really think of the intense, long lasting fire fights we saw in AFG.
On a side note, AFAIK later generations, although I don't know which exactly, transitioned from rifeld to polygon barrels (?) which should be somewhat more heat resistant. I don't know what the deal is here.
Now the issue is with procurement stopped last summer, we're on the verge of running into yet another equipment shortage. The first batches, introduced some 15 years ago, start to reach the end of their service life (the barrels in particular) after seeing some instense service abroad.
The A2s brought the shorter but stock, a new reflex sight, and I think the hand guard may come with picatinny rails.
The A3s are the IdZ-ES (Infantryman of the future - expanded system) rifles with a new telescopic sight, accessories and PTT buttons.
And then there's the A4 concept wich is ment to be the new base version, while the A2 and A3 are still based on the A1.