@musugru, welcome to the community forums.
Based on this topic:
can you post the output of
btrfs fi show
you could also take a look at this:
http://rockstor.com/docs/data_loss.html#data-loss-prevention-and-recovery-in-raid5-6-pools
The Rockstor/Kernel version is unfortunately quite old, too. Some of the RAID5 stability (and the associated rebalancing operations) has improved with more recent Kernel versions.
I leave it to @phillxnet to offer additional advice, since he has been dealing with a few of these in the past.