There is no procedure that involves cutting off fuel to both engines while in-flight; one at a time, but not both. Then, there is no procedure that ever involves touching those controls during takeoff. Finally; there would be communication between the pilots discussing any such troubleshooting, they wouldn’t just take it upon themselves to start flipping switches without at the very least letting the other pilot know what they’re doing. Particularly when it comes to troubleshooting; there is a strict set of checklists they go through as a team, with one reading out questions, the other responding with data/answers from the instruments and the first confirming that response.
These were both experienced pilots with ample flight hours; they knew what they were doing at those controls. I’m not going to throw human error out the window entirely, but it’s not looking very likely unfortunately.
Either that plane was brought down intentionally, or there was a stunning error in judgment wildly disregarding procedure in that cockpit that was not communicated at all. (note: the mics record to the blackbox continuously, they’re not ptt, if one of the pilots had said something, it’d be on the tape.)
You can’t exactly expect a plane to keep flying when you’ve commanded the engines to stop running/taken away their fuel at such a critical time…