Hi, i have same problem. Actually it happen sometime after win10 updates. I think it is related to windows (Host).

My workaround.

1. suspend all guest

2. open virtual network editor, change setting

3. export setting (one time only)

If ping timeout happen, just import again. Haha, every time i did this funny thing.

FYI, if you reboot host (Win10), this problem is not happen. Maybe some cache is still there. If you shutdown or sleep for a longer time this problem arise.