I have a rig with 13 RX570's (8GB) and I'm seeing significantly slower hash rates (MNX) with v0.6

lolminer-v0.5:
Average speed (30s): 15738.2 sol/s | 15461.9 sol/s | 15441.3 sol/s | 13329.1 sol/s | 15433.2 sol/s | 13315.9 sol/s | 15378.7 sol/s | 15398.7 sol/s | 13290.2 sol/s | 15388.7 sol/s | 13264.9 sol/s | 15362.0 sol/s | 15379.7 sol/s Total: 192182.4 sol/s


lolminer-v0.6:
Average speed (30s): 14536.5 sol/s | 14390.1 sol/s | 14360.5 sol/s | 12398.3 sol/s | 14329.5 sol/s | 12365.6 sol/s | 14288.8 sol/s | 14240.7 sol/s | 12301.1 sol/s | 14282.0 sol/s | 12367.2 sol/s | 14294.6 sol/s | 14224.2 sol/s Total: 178379.0 sol/s

Both are using identical settings which include 'Work batch: 14'
If I go any higher than this, I see the following error message (with both lolminer versions)

terminate called after throwing an instance of 'boost::exception_detail::clone_impl >'
  what():  conversion of data to type "i" failed

**Damn, I was hoping that would be fixed in this version

Any clue as to why I'm seeing the slower hash rates with v0.6?