Straight from the Boeing Non-Normal checklist for Dual Engine Fail -
"Engines may accelerate to idle slowly. Slow acceleration may be incorrectly interpreted as a hung start or engine malfunction. Any further cycling of the fuel control switches will result in longer start times."
(Emboldened emphasis mine).
That's for RR Trent engines, procedures may differ for other engines on the B777. Hope that this helps.
Regards,
Old Smokey