Odd hundreds of amps when switching on braking after adding braking resistor to H-bridge
You state the differential load (ie the motor) has a resistance of 10R and equally you have a DClink voltage of 30V.  

If you were to permanently turn on a diagonal pair of switches you would only draw 10A from the supply. 

Now if you were to turn both switches on in a leg (bad control or no dead-time added to mitigate switching times), then you would present the battery with a "short-circuit" and thus a significant amount of current could flow.

Plt the drive signals when such current spikes occur, I wouldn't be surprised if there is some overlap