For the combat case, Carriers combat is implemented by temporarily adding fighters to your fleet, then removing them. During that temporary period, your effective range is decreased, but it has no real impact on the combat or your movement thereafter.
Not sure about your explorer case.
- Did you use a wormhole and leap outside your range?
- Did your explorer join a fleet with a shorter-ranged ship?
- Did you decommission/destroy/trade a planet or starbase?
- Did you trade away a bunch of the +Range trade goods?
- Did you select a different ship (which will have a different range line)?