Hi, just to update you with this, and sorry its taken some time, but we have finally resolved the issue with this item.
1 - The reason why we could not reproduce the issue is because we were test flying the drone on 2s (as it didn’t have the O3 installed we didn’t need extra power)
2 - When we moved to 4S, we could reproduce the issue, however because it only occurred on higher voltage we investigate further and it turns out that the PID D gains, we also turned down the D term lowpass filters as they were set rather high, so we lowered them too and now the quad it flying flawlessly on 4S too. Could you confirm which voltage you were using on your quad so we can double check this too.
Based on this the issue was caused by misconfiguration, and not a direct hardware fault, however, the turnaround time for this issue has gone on for quite some time, so I just wanted to check if you prefer us to send it back to you again, or do you prefer to look at a refund?
Please let me know so we can get this issue closed for you at last!