DBCC DBINFO incorrect dbi_dbccLastKnownGood
READ ONLY REPLICA (Asynchronous AlwaysOn HA AG)

Like Erik pointed out, AG Replicas are currently read only so it can't update the values here. Additionally, if it did update the values it would just be overwritten the next time anything was updated on the primary and the log block sent to the secondary.

I decided to check the PRIMARY REPLICA where DBCC CHECKDB is also running 
•Subplan ran at 02/05/2018 00:00:00 AM successfully, with a duration of 02:14:40
•When I run DBCC DBINFO('myDB') WITH TABLERESULTS I see dbi_dbccLastKnownGood  02/05/2018 00:00:40.113 which is the same as the RoR but it should be 02/05/2018 02:15 AM

The job started 2:14:40 ago, which is the time of the last known good checkdb - that's true. You started it then, it ran for 2 hours and 14 minutes +/- some agent stuffs. The times look fine to me, it's not like the job ran for 5 seconds and shows a last good of 6 hours ago.
I believe the issue is you expect the CHECKDB to show the good value at the end of the run versus being updated when it was executed. That shouldn't be a problem.