In the OMV browser window, in the Processes tab, hit the refresh button a few times. (This will give you a capture of what's happening at that moment in time.) At some point, you'll see 100% CPU utilization. So what do you think that might that mean? Everything can't be handled, so tasks are delayed or ignored until the CPU catches up. 100% is 100% - there's nothing left to give.
Try to be realistic about processing performance of a $30 device. If an R-PI was as strong as you appear to want it to be, for $30, they'd be in data centers.