RG750G after upgrade 6.0.rc6 droping

Hi, i have this router RG750G and after upgrade from 5.17 to 6.0.rc6 he droping the internet traffic
from eth1 on every 5 min for some seconds.
I try to downgrade from system–>packages–>downgrade–>reboot

but nothing the soft version is the same.
Can someone tell me how to downgrade
Or is it possible to upload files from version 5.22 and after reboot to downgrade it.