Welcome to the PLCTalk forum community !
What is the scanning device (1747-SDN, 1756-DNB, etc) ?
Are you connecting to the DeviceNet network by passing through a PLC backplane module, or via a direct connection like a 1784-U2DN or 1770-KFD ?
How large and how busy is the network ?
Have you assessed the network for signal problems ?
In general, class 3 messaging like "going online with a drive" is by design a lower priority than Class 1 I/O messaging, and should perform more slowly rather than delaying the I/O messages.
And even the old 1203-GK5, and certainly the 20-COMM-D, can easily handle unconnected messages (parameter upload/dowload/monitoring is done through the Unconnected Message Manager (UCMM) object) without faulting the I/O connection.
But networks that are already heavily loaded or have signal problems that already generate a lot of retries, could collapse under the load of even light-duty messaging like going onine with a drive.