Pilot reported understaffed and overworked controller may have caused a traffic alert; rejected takeoff; and long delay for the next takeoff at FXE.

Narrative

I was conducting full stop taxi back night landings at KFXE for my commercial certificate. On the second take-off; I was given a take-off clearance; right traffic Runway 9. I began the take-off roll. At around 50kts; FXE Tower advised take-off clearance cancelled exit Taxiway A4. I immediately pulled power and acknowledged the clearance cancellation. The canceled clearance was apparently due to another pilot that was disoriented and may have been in the runway environment. I exited at A4; however to do so; I had to apply heavy breaking and subsequently skidded; using all available paved surface. I was cleared back to Runway 9 on Taxiway A.The issue is that there were multiple arrivals; multiple departures and multiple aircraft in the pattern. The lone controller had all frequencies combined; Tower; Ground; and Clearance Delivery. She was doing a great job but the workload at that hour is way too much for one controller; not her fault; but the facility should properly staff for the demand of that airport. At one point she cut a new ATIS on the frequency stating it was the only way she could get that done. Having one controller at FXE on a Friday evening with the mix of turbo jet; twin and single engine propeller aircraft is not safe. Thank goodness; this was caught and I did not continue the take-off roll and collide with another aircraft. Please encourage FXE Tower to staff appropriately.