After upgrade to 8.0 I am unable to get any stats which means Applications tab doesn't work and just kicks out an error and same thing for most everything under the Monitoring tab.

What did I try?

1. I removed the BIG-IP device and readded it with same results
2. I removed DCD and readded it back in which took about an hour each because it would hang on ES_ service

What worked?

These steps will only affect the configuration between the Big-IQ and the DCDs, none of the Big-IP data should be affected:

1. From bash on the CM:  reset-data-collection-cluster
2. From bash on each of the DCDs:  reset-data-collection-cluster -es
3. Re-add the DCD devices

It is important that we use the -es flag on the DCDs and NOT on the CM.  This is because we want the DCDs to control the data that the CM knows about, rather than having the CM determine what data it remembers.  After completing steps 1 and 2, try adding the DCDs back to the CM.  If this doesn't resolve the issue, isn't anything more we can do to preserve the previous data and we'll need to go through these same steps without the -es flag on the DCDs.  If there is no value in retaining the historic data, we can remove the -es flag from the second step the first time.