I have tried several projects with multiple components (imported or within the original project) that the Merge Combined step won’t process in because it says there is a single incomplete component in the project. I’m running the version on STEAM.
hello, can we please see a screenhot of the error message?
It does not come up as an error dialogue box, it just says under Merge Component that there is a single component in the project when there are several (and trying to align the components using F6 or the align button fails, even if align components only is turned on).
please excuse getting back to you just now,
this notification in the Help section actually shows up when there is at least one incomplete component in the project, which is the one in that there are fewer images registered than the whole number of images it could be aligned from,
so component with 39/39 cams would be classified as complete, while anything less than 39 cams is classified as incomplete,
I believe that you could do much better without trying to merge such small components and rather try to align this small dataset solely from the 39 images, without these imported components, and if it does not suffice, follow the tip from the Help for this specific case, which is a piece of advice to add more pictures,
you can - then - also try using control points if adding more pictures is not enough,
sometimes it is necessary to reshoot the scene completely and get a dataset of better quality though
EDIT: corrected my grammar mistake 
This is happening for several photosets that I’ve stitched successfully in photoscan- they were shot on a turntable and several have top and bottoms that need to merge. In the case of models where it is not recognizing the top and bottom components to merge them, how should I proceed?
even when the images are the majority of the component I saved it from, it still does the same thing-
You can use control points to merge both components
With control points you can manually create a link between two or among more images. You have create at least 4 control points, such that all of them are assigned to more than one image in every component
this is not about majority - the Help advice in the rectangle would disappear only if you had a 237/237 component in the project and at the same time there could not be any other component(s) consisting of less than this number - as explained above,
how did it go with the control points Rafa and me referred to?