songevan,
There might be a loose magnet in the hall sensor in the brake. You can remove it with some fairly intensive surgery, there are videos on youtube if you search for ES2 Repair Throttle that will show the general procedure.
Just don't do what I did, and accidentally let it tip over.
Bent the throttle lever up somehow 90° up from where it should sit and in the process ripped the sensor off its leads entirely! ..A very slow wait for a package on a slow boat from China now...