All HEIC images became blank in Photos app

Did you use any cleaning application to save storage? Not all are save to use and can damage a Photos Library.

If i export photo as "unmodified original" it is ok

Then try to fix this by exporting and reimporting.

• Export the unmodified original for a broken HEIC image. Test if the export is o.k.by opening the HEIC image in Preview.
• delete it from the library and empty the recently deleted album.
• Then reimport the exported photo.

Can Photos now open the HEIC image againß

Have you enabled iCloud Photo Library on your Mac? Check the preferences in Photos, if this setting has changed. Is your Mac syncing with your iPhone using iCloud Photo Library?

When i opened a photo it loads hi res edition for a few seconds, then became blank (but with detected earlier faces on it). I

You may need to repair the thumbnails..

Select a few of the white photos, then enter the key combination ⌘R to rotate them. Then rotate them back with the key combination ⌥⌘R. Frequently this will force the creation of new thumbnails.