Thank you for reaching out and sorry to hear you're experiencing issue with your icon assets. Could you please share some screenshots for better understanding? Please also share the version of XD and the OS details.
OS: Mixed, my team have experienced the same on both Win10 and MacOS.
This is client work so I will have to use a discreet example:
Below is an example of what a component looked like before the update.
And after the update:
As you can see, some icon assets have dissapered and some have reamined. There is not difference in how they were addded to the design, all icons are drawn from the same Ai icon library and in this case they are all part of a larger component.
This is one example, it has occured on pretty much every page design we have and across multiple project streams and design files. As best we can tell, it would seem that any icon that was a compund shape was removed and icons that still had editable paths remained. So in any instance where an icon was edited or custom made, it remained, and instances of icons used straight from the client icon library have been removed.