How big was the cloaked ships list?
On of the issues with the current UI is if there are too many types of cloaked ships on a planet, they list themselves off the bottom of the screen and there is no indication they have done so.
To handle this, get your scout starships and run them over every resource point, you will probably find the guard post.
Occasionally guard posts are off by themselves and not on a resource point, but most of the time they are.
Note that scout starships have a small Tachyon Emission range (what reveals cloaked units) so you will want to give them the move order to directly on the resource point.
If you want a bigger decloaking range, the decloaker (on the Support tab) is your only option, although as of the last patches it can now hold it's own in combat as well as having a large Tachyon Beam range.
D.