Hi Omar,
If the throttle is not drawing too much current, then it must be a weak +5V supply from the controller.
If it is under warranty, you should contact your supplier and explain the problem.
Otherwise, I would suggest testing it with an external voltage supply from 3 x AA batteries in series connected to the Red +5V supply and Black ground connection on the pedelec cable.
If this cures the problem, I would suggest that you find a
suitable DC-DC converter that can work off your main battery, with the output set 4.5~5V to replace the AA batteries.
Alan