After I upgraded ES and LS from 2.0 to 2.1 and Kibana from 4.2.1 to 4.3, everything seems to work fine except nodes monitoring information collected by marvel agents. I used to see hostnames, now I can't tell which is which... How can I fix this issue??? 
Can you try deleting the .marvel-es-data and .marvel-es-2015-12-14 (just the most recent index - it might be 2015-12-15 by now). There was an issue when upgrading where the mappings of the current indexes weren't updated.
We're fixing this upgrade issue in a patch release soon, but as a workaround, deleting the current marvel index allows it to be re-created with the new mappings.
I tried deleting .marvel-es-data and the most recent index. Still experiencing the same problem....
Never mind, I missed one step. Deleted .marvel-es-data and the most recent index again and went to kibana, now everything looks fine. Thanks!