In rare cases, with some old flashes or some Yongnuo models, it could happen that the flash fires just one time, then you have to disconnect and connect again the cable between the flash and the trigger.
This doesn't indicates that the trigger is defective, but the reason is that the flash get too much current from the trigger.
Anyway, it's quite simple to fix this behavior. You just need an inexpensive adapter (2-3 Euro + shipping, less if you assemble it by yourself). The adapter must be connected between the trigger and the flash.
This is the schematic if you want to assemble it by yourself:
Note : if your flash has a low trigger voltage, you could use a capacitor with lower max voltage value.
Be careful if you own a high voltage flash (> 60V): you need a capacitor with higher max voltage or it could explode! In this case you could even consider to build an high to low voltage adapter.
An alternative way to mount it is to solder the two components inside an hot-shoe adapter:
If you need more info send me an email.