I own a TRANCE E+ SX 1 PRO and had a similar issue. These are the steps that my local dealer went through to get it fixed over a number of shop visit
1 - Adjust the speed sensor
2 - Replace the speed sensor and cable
3 - Adjust the speed sensor by making it closer to the magnet
4 - Replace all the cabling
5 - Finally Giant said to replace the entire mote and since I have no problem.