IoT Cloudwatch Metrics for Dynamic Thing Groups

Here is one approach:

There is an IoT Core Metric called "AddThingToDynamicThingGroupsFailed" which will likely allow you to achieve what you are attempting.

You could set up a CloudWatchAlarm to evaluate this metric for value change, then use that to trigger your logic. I haven't tested this, but here is the CLI format I would use (YMMV):

aws cloudwatch put-metric-alarm
--alarm-name "AddThingToDynamicThingGroupsFailedChangeAlarm"
--alarm-description "Alarm triggers on increase in number of failed additions to DynamicThingGroup"
--metric-name "AddThingToDynamicThingGroupsFailed"
--namespace "YourNamespace"
--statistic Average
--period 60
--threshold 0
--comparison-operator GreaterThanOrEqualToThreshold
--evaluation-periods 1
--datapoints-to-alarm 1
--treat-missing-data notBreaching