Hello,
Thank you for reporting this issue.
The problem was that the zone class was not loaded when displaying the variant editing form, so when a variant had a zone-restricted price, the page would crash with a fatal error "Call to a member function get() on null". As you noticed, the price data was saved correctly to the database before the error occurred on the page reload.
We have fixed this and updated the package available for download in your HikaShop account. You can download and install it over your current version to apply the fix.