Home Sharing may be limited to 1080p, 30 fps. Do any of your ‘missing’ home videos exceed that? Try converting a missing video with those constraints, and then adding the new version. Does that show and play better?
One film does have slow motion film in it.
The slo-mo effect from an iOS device is a ‘soft’ file property, the actual footage is high frame rate, and the playback changes frame rate for the effect. The start and stop moment of the effect is still editable. It may need conversion/export to constant frame rate for compatibility with other playback software and systems.