Ouch.. tough reply.

Maybe put he CG back more. make sure your up throw is maxxed out, doesnt take much down to make most planes go mad. can your servo(s) hold the up power?

Bipes tend to need a bit more entry speed to pull off a clean snap roll and/or lots of power,perhaps do not cut any throttle much and follow thru.

Prop selection can be critical and I would also look at that. Also check the incidence on the wing (s) and tail are correct.
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