Neither speedhacking nor autobitsetting could have any direct effect whatsoever on the results of the burn, since neither of them touch the write strategies or any of the write routines--it's simply not possible.
Possible causes of "it worked before but not now"
1) Did you burn at the same speed both times?... speedhacking does affect burn quality if you use a higher-than-rated speed (SH gives you the option to burn faster, but unless you actually order your software to make use of that option, SH has no direct effect on quality). Burning at the same speed, SH or no SH, has no difference.
2) What was the firmware revision before and after? If in the process of patching your FW, you decided to go to a different firmware revision, that could cause problems.
3) Is is the same media type as what you burned before? From the same spindle?