There are few reasons why your sliding gate might stop working after rain. Firstly, there might be possible that dirty stuck on the gate rails. Inspect your rails for any visible obstructive objects. Secondly, check is there is power to the gate motor. There might be possibility that power tripped and batteries are flat, which if that’s the case also consider replacing the batteries. Power to the gate might trip if water went into power cables which are exposed or not properly insulated. Thirdly, check if the actual gate motor electronic components were not exposed to rain, which might have damaged the circuit or damaged by lightning or power surges.