Team,

Some of the delays you 'might' be experiencing in some of the styles could be indeed due to any of the reasons you've already listed above. In the SD1/X units, I do believe though that the GROOVES do have a part to play with what might seem to be a delay when in transit from a FILL to A, B, C or D. For the most part, in order to avoid such, most of the FILLS have been programmed to carry forth the groove used in the previous ARRANGER part. Eg the DRUM2/GROOVE track of FILL_1 will be what was used in ARRANGEMENT_A. In cases where these vary, you might notice a slight 'glitch'. Since they are LIVE-DRUMS, they really cannot accurately be QUANTIZED because that will then defeat the purpose and eliminate a lot of that 'human' aspect.
A way to reduce this effect would be to turn OFF the AUTO-CRASH. This way, you'll experience a 'smoother' transistion b/w fills and other arranger parts, the reason being that the AUTOCRASH is programmed right on the note. Should you be using eg a LATIN rhythem that's made up of mostly GROOVES (which are not strictly QUANTIZED), there could be a 'clash' in transition.
Hope this helps ... at least from an understanding point as to why.

AJ