Do you have any related errors messages in the IAP logs or on the switch port? In the first instance to rule out a hardware fault, swap one of the working IAP's to use the same switch port. I would also check on the switch that there is enough power available for all of the IAP's.
There is numerous reasons as to why a single AP can reboot, whether it is hardware of software. Do you have a syslog set up to capture any output? It might also be worth attaching a console cable to the AP to capture any output when the AP reboots.
When the IAP is "down" on the VC, do you have any L2 or L3 connectivity to it?