Remove only one of the denied hosts and monitor the logs that have its IP [ IME is great doing this ].
If you identify the host as a malicious unit, move it back to the list.
If you find out that the IPS is reacting to false positives, you can check the signatures that triggger and see how reliable they are.
A packet capture is also a great idea to see what is the unit is seeing and understanding why it is blocking it.
Finally, if you just don't want this host to be affected by the IPS rules, simply create an event action filter for it.
