Try putting the display in a bag of rice for a couple of days, it will draw out any moisture.
The motor is a direct drive. They are notoriously punishing on batteries. With a 25A controller the battery needs to be capable of delivering at least 30A so as to be not stressed/damaged by the current draw.
You say that when this starts to go wrong you hold the power button and get full power. In this state you will be drawing the full 25A. If the battery is either not fully specced or is ageing it will suffer voltage sag. If/when this reaches the low voltage cut off of either the controller or the battery management system, then all power will be cut.
It is a common occurence with these large direct drive motors. They need big batteries with top class cells and so are very expensive.
Can you measure what voltage the battery is when it has just been charged?
Can you measure the voltage when it has just cutout?
Hi I have never reached voltage cut off I don't think, had the battery indicate 3% left on the display when heading home once or twice but settle it jumps back up to 25-30% so under big loads there is a bit of voltage sag, in lower powered modes do manage about 3 miles with the display remaining at 100% tend to sit it on lvl 3 and that sets a speed of 13mph
When the display switched off I was in mode 2 drawing 3 amps, I display amp draw when out for a long ride, it cut at about 60% remaining at 51 volts as I did cycle the display when it came back on.
So it was fully charged yesterday morning so has sat all day and night and the volt meter reads 53.9v so it is missing a little I think but not alot
So I am right in thinking if I was to change the controller and drop to a lower amp output the motor would be slower but would cause less voltage sag or do I need to stay with a 25 to 30 amp due to the type of motor ?