I found rather early in the semester that the syllabus was going to be impossible to rigidly adhere to. Thankfully I had included language in my syllabus that reserved my right to make any changes to it whatsoever.
The first major hurdle I encountered in keeping to the schedule on the syllabus was that textbook acquisition was not a timely and uniform activity, it came in trickles. Neither the carrot nor the stick sped up the process. Frustrating as it was, there was little I could do until the class had reached critical reading mass, so to speak.
The second major hurdle I encountered was a disastrous final draft of Essay 1 in both my sections. It was so awful, I made the classes re-execute it. That certainly fouled the schedule.
A repetitive problem in keeping to the timeline on the syllabus was submission tardiness. If more than 40% of the class showed up on a Monday without the drafts for peer review, the most efficient use of the class time was not peer review, so that got bumped.
In the end, the work all got done but it was done in different sequences. My take away after this semester is that a syllabus must be fluid, not rigid or things may fall apart.