This issue is fixed via software in NOS5.0.2c.
BNA was receiving error because VDX DCMd daemon went into faulty state. VDX DCMd got terminated because it tried to access un-allocated index memory.
The issue is only when we perform firmware downgrade using BNA, as netconf/BNA request [fwdl-status] encounter this code path where count has incorrect value. FWDL using CLI we dont hit the issue.