RX 470 Rate drop HELP!

[Heppe]

Hi there,

few weeks ago i started mining Eth and SIA with Claymore miner.

I run 4 Cards RX 470 and everything went well till one card got blown up.
Since then one of the three remaining cards is at only 4MH/s instead of 20, like the other two.
It isnt a specific card, if i unplug one card, the other two are doing well, with 20 MH/s
Everytime is start the miner one GPU needs longer at the Point "GPU DAG creation Time"
Two cards need 4000ms and always the third needs 12000ms.

Can anybody help a noob ?