Modbus device disconnected but can be read from read test

[khalil]

Entries without mapped objects are not polled.

thank you admin 
another question
how the SL,LM poll mapped registers one by one or as a group.
if it pulled one by one, is it possible to make a group poll to decrease the traffic?

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please advice regarding these errors,
 two Modbus RTU devices keep connecting and disconnecting