Exchange DAG DB copy seeding fails

I have Exchange 2010 DAG setup at two sites. Primary & DR.
Out of all 10 databases 2 databases are failing in seeding. Each having size around 300-350 GB.
Seeding failes after ran for almost 220 GB Then we need to reinitiate it again. Can someone help me to troubleshoot issue to find out the reason & resolve it. Really frustrating to start all process again from start.

Second issue is today for few databases copyqueue length is not reducing by single but database copy showing as healthy. Please help which event log i shud monitor to find out the cause.