We used to have this issue all the time even before insight start having issue.
I will suggest to look for how this is trending over time and try to understand who both system flag as bounce and the system measure of sessions.
Over the past couples of years I came to work very close to both systems are there are measure I take at face value in each system and others I won't even consider.
There are some Topliners thread on the topic
Re: Eloqua VS GA VS other paid analytic package
Good Luck
