Just to reassure you, I had a similar problem involving FBB forwarding.
I tried altering the number of buffers with z8530drv.conf (this feature is
mostly undocumented) unsuccessfully, so cheated and altered the default
setting in the code. That, together with extending the maxkey time which
was occassionally being exceeded, fixed my problems. The number of TX
errors on sccstat dropped greatly, and my forwarding problems vanished.
73
Steve, vk5asf