We just upgraded one of our M1000e chassis to CMC version 6.1 and have a strange issue with upgrading the iDRAC firmware of the blades since then. Upload of the iDRAC firmware package seems about 3-4 times slower than chassis' that are running 6.00. With 6.10 the upload is around 49% after 30mins which is the default session timeout. We don't have this issue on the chassis' that haven't been upgraded yet (which we will postpone). A manual/extra failover of the CMC doesn't fix the issue, upload stays slow.
What I would suggest is to backflash the 6.1 system back to 6.0 and then retest the iDrac upload from there, this will test if it is the 6.1 update causing it, or an issue with that specific systems settings or configuration. Also, would you clarify the generation of the blades installed as well, as this will help us to isolate the issue.
Lastly, if you have any chassis logs or racdumps let me know and I can have you email them to me.