RX480 suddenly goes to 0.8 mh/s or less

Hi

I've set a new rig with 2 RX480 they currently mining at 22.7 mh/s which is two low for myself, trying to get it up, but got with one of the Rx to drop to 0.8mh/s. I need to reboot the system in order to get it again on 22.7mh/s.

Thanks in advance for any help.