If you run in parallel the total current of the driver is divide between all the parallel rungs.
If one of the rung has problem,this same current of the driver is now divide between all the existing rung
minus one.
Hence the current through each rung now is higher .
If this is uncheck or not notice in time, the higher current in each of the running rung now generate more heat.
which if not check and exceed the optimium temperature of the LED will deteriorate or shorten the life of the LED.
This process will continue if left uncheck till all the LED is overheated and burnt out.
Unless you have proper protection circuit in place for each rung it is not advisable to run LED in parallel.