Ah, well I can help ye with that problem. ;3
Sometimes if exported object groups from different maps 'ave the same name, FH replaces the oldest file with the new one ye place in exports. Since this object group file is only f'er one map /group/, the other maps using the same object group cannot load their version of the file, causing objects to "disappear". Unfortunately, ye will just 'ave to choose which exported object group ye want in the exports folder or ye can swap 'em out when y'er using the other maps.
Hope this helps. I'd be happy to elaborate if any of this is confusing.