Hello,
are you 100% sure that this issue is bucket-related? If so, it is possible for us to share a development command string with you, which is an internal option and using it may have some unexpected consequences and it may be changed or removed in the future without notice.
We are aware of one issue with bucket rendering which introduces a small slowdown towards the end of a batch of buckets rendered, and we are working on a fix.
Thanks,
Jan