Unfortunately, I can't explain why some helmets don't function well in that mode, but, I use a Speedglass 9000X which has two modes.
One for GWAW and SMAW, and a mode for GTAW. Additionally there is a sensitivity adjustment knob, if you "tweek" the setting so it just turns on with existing light conditions, I have yet to have the "flickering" problem. If I am in an area with multiple welding arcs (field work), that can be a problem, then I just turn the sensitivity all the way up, finish my weld and go find a welding curtain, safety issue anyway. I use this helmet mostly with Miller Dynasty's, but have had significant hours on the bench with Aerowaves; no problem so far. One of our welders has an Optrel that seems to work well for him also. I'm guessing you have tried a 9000X, just wanted to point out that sensitvity adjustment, it matters a lot.
Best regards, Brad