Since monday, average dropped to 100GHz most times even lower.
Thanks in advance.

Have you tried resetting the U3's (unplug both power and USB) and then restarting CGMiner?
Yes I have rebooted all hardware.
Removed power and usb cables.
Tried with other cables. All the same.
Plugged USB cables in different USB ports.
No difference.
Most of the time 115/120GHz that is pretty good I believe.
Since monday, average dropped to 100GHz most times even lower.
GHz? Do you mean GH/s? The hash rate, not a measure of frequency.
There is no answer, U3s do what they do, be lucky you have two that work at the same time.
LOL

yes I mean GH/s. Sorry.
I guess I mite be lucky then. It took a lot of trial and error and a decent hardware computer:
https://bitcointalk.org/index.php?topic=827356.msg11803834#msg11803834If so, switch the higher hashing one's power supply to the lower hashing one and see if the hashing rate on them changes around also. If the hashing switches, you need better power supplies.