The symptom we had, was one or more drives would just drop off of DNet for a period of time. In a 24 hour day, each drive would drop out several dozen times, for less than a second.
Occasionally, a drive would drop out for 5 to 10 seconds. This became noticable. Once in a while, more than one drive would drop off for an extended period. When they both tried to come up again (on DNet), all of DNet locked up, and required a powerdown cycle to get things running again.
If you are monitoring the actual DNet comms status to each drive, I'd bet you would be seeing lots and lots of short duration dropouts.
If indeed it is another problem (what is the scanner status during a drop?) you should probably check all of your connections and terminators.
Also, make sure the 24VDC DNet supply is in good shape.