Are they movable track lights ?
Or stationary ones ?
If they are movable, its possable the contacts
between the light fitting and the track are dirty,
so not allowing the power to get thru.
If so slide the light backwards and forwards in the track
a few times, and see if it improves.
Some proper contact cleaner and lube will help.
Dont use wd40 or crc.
I dont know if you have this brand,
But you would have something simulair.