We are observing a likely bug in DayPilotPro-7.1.2730 with TimeHeaderCellDuration. If the TimeHeaderCellDuration doesn't divide evenly into the Calendar Display time range when you have it limited then a js error occurs and no cells are rendered. I presume that this is caused by the partial time range not being handled.
CellDuration = 20
TimeHeaderCellDuration = 40
BusinessBeginsHour = 8
BusinessEndsHour = 17
This will cause the following js error and no cells will be rendered: TypeError: this.hours[i + this.autoHiddenHours()] is undefined
Changing BusinessEndsHour to 18 will fix the problem. As would changing BusinessBeginsHour to 7.
I haven't verified this, but I'd guess that if you had DayBeginsHour and DayEndsHour set in a similar manner as above, plus Enums.HeightSpecEnum.Fixed, that this would also cause the same problem.