Same for me... Even now on iOS14 and Catalina 10.15.7 it is not working for months now...
This is absolutely annoying!
Here are some logs:
standard 19:34:44.779180+0200 Photos 			 IMG_1103.HEIC | Download Complete
fehler 19:34:44.779486+0200 Photos ERROR: Der Vorgang konnte nicht abgeschlossen werden. (com.apple.ImageCaptureCore-Fehler -9956.) (, path: 1C4D0D82-827A-4DF7-89C8-C1F1A5FC7D15.HEIC (IMG_1103.HEIC)), file: PHImportDeviceAsset.m, line: 539
fehler 19:34:44.779583+0200 Photos [IMPORT ERROR] <private>
fehler 19:34:44.792818+0200 kernel Sandbox: PTPCamera(3381) System Policy: deny(1) file-write-create /MY-PATH/Fotos-Mediathek 4.photoslibrary/external/com.apple.Photos/import/145CLOUD/.tmp_IMG_1104.HEIC_
standard 19:34:44.854583+0200 PTPCamera 						icdevice | Failed E: 0x139bba/ A: 0xfffffffffffffffd - Received an invalid transaction size
kauki
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