Did you make sure if you had any extra groups of objects that you put the .fho file in? That allows others to see the objects for example:
MyTreesExtra.fho
The object files that are classed as "OBJECT file" to the right allow you to have the options menu in map maker, hence in exporting this file is not needed.
Also, if the normal .fho file does not work, you can go to object maker to try and re-export them, just click of one of the object in the folder and then export and it will export the whole folder. The .fho file for the object folder can then be found in "exports" (due to overwriting reasons, I suggest you move everything in there into a temporary folder so as to get the .fho file separate.
Try replacing the old .fho files with that, hope this helps
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(Sorry if you had already figured this out)