Indeed. It is not a Viggen - only problem, but rather a DCS 2.0.5.2576 Update 1 problem.
I have spent the better part of the morning testing, here the results:
A-10C = Perfectly O.K.
AJS-37 Viggen = Crashes down to the ground (gear up), gear goes down again, but the plane is damaged and the engine goes off, fuel, in spite of the full external tank = 0%. If starting in the air, it trims uncontrollably up, 20% Fuel (Only the fuel of the external tank, I suppose).
BF-109 = Fuel on 0%, just managed to take off, then engine blocks.
F-5 = Freezes completely DCS, CTD, regardless if in the air or ground.
F-86 Sabre = Perfectly O.K.
FW-190 = Exactly the same behaviour as the Viggen.
KA-50 = Perfectly O.K.
MIG-15 = Perfectly O.K.
MIG 21 = Perfectly O.K.
Mirage 2000C = Fuel OK, though no way to go to afterburner, even with the throttle full open. It stops at 84 instead of over 240 fuel flow. After about 30 seconds in the air, it trims uncontrollably up, like the Viggen, but much worse.
P-51 = Perfectly O.K.
SU-25T = Perfectly O.K.
By the way, I have uninstalled and reinstalled that VC14 Runtime Visual C++ 2015 Redistributable Update 3 as instructed in the changelog.
ED or moderators, please advise, or acknowledge.