I've ran into this problem a couple of times and always found a workaround, but I would rather address the problem that continue using workaround.
Short version: Sometimes I can't select construction geometry created in a sketch even when I have the sketch set to "show".
Long version: Scenario #1:
I am editing a sheet metal part with with holes created by extrude cut. I wanted to replace the holes created by the Extrude Cut feature with a Hole Wizard feature. I changed the circles in the sketch which created the extrude cut to construction geometry. Then created a Hole Wizard feature on the same surface, with the location points in hole wizard coinciding with the circles in the sketch. It worked perfectly. Second step was to create an alternate configuration with a different hole type. So I suppress my Hole Wizard Feature create a new Hole Wizard Feature, and repeat the steps above. However fo some reason I cannot coincide the holes with the any construction geometry in the sketch. I try and try again Hiding and showing the sketch for some reason no matter what I do I can't create any relations to the sketch construction geometry.
Scenario #2
I have a part to be brought into an assembly. The part needs to be spaced at exactly 15" in an array but the part itself is slightly less than 15". So when I created the part I added a construction geometry
15" box around the the part. I bring the part in and I mate one side to another part using the construction line I created in the sketch. This works perfectly. My next step is to mate the top edge using the same method. For some reason Solidworks will not allow me to select the construction geometry to create a mate.I've been able to work around these problems and continue but I would like to know why I can select construction geometry only intermittently. If I create a simple part to test this issue I never run into problems it only happens with more complicated parts.
Anyone have any idea what I'm doing wrong.