Maybe you should try to fly in rate mode: if vibrations are causing a lot of gyro bias, the artificial horizon is slowly accumulating a lot of offset, then the aircraft may "bank" pretty severely. Had this issue with a pikoBLX but never experienced this with a brainRE1.
In rate mode, artificial horizon, is not used: so if it flies correctly in rate mode, this is it.
As suggested by Litterbug, you should either enable buzzer alarms, or record the OSD footage. In case of a problem the buzzer can issue morse code explaining the error: "B" code is for battery, "G" for GPS, etc... Same story for the OSD: if you enable system alarm, you will see a blinking text in the video feed.
Memory is also an issue: you should not try to enable too many modules at once. As far as I am concerned OSD and Full bore logging was a big No-No. So disable logging, autotune, navigation, TxPID, etc...
Last but not least, the mpdb only provides 1amp BEC. Depending on your accessories you're probably maxing out the capabilities of this board. For instance telemetry receivers and LEDs are quite power hungry.
This board flies great, but it has limited BEC and memory... Hope this helps