Hi Stephen,
What kind of elements are deleted when you re-share the project? Can you also recognise any element what is missing then and is visible easily (e.g. stair, wall)?
It is possible maybe there were corrupted elements in your local cache what ARCHICAD tries to fix somehow. I can imagine many of these items are not even visible, due they don't have thickness or length.
Kind regards,
Noémi Balogh
Customer Engagement Expert, Community Admin