Debian loader repeatedly fails on some packages, generating thousands of partial visits

Example of affected packages:

 65612421 | deb  | deb://Debian/packages/netrik
 65621554 | deb  | deb://Debian/packages/robotfindskitten
 65640406 | deb  | deb://Debian/packages/drbd8
 65639256 | deb  | deb://Debian/packages/drbd-utils
 65633240 | deb  | deb://Debian/packages/jaraco.itertools
 65619771 | deb  | deb://Debian/packages/vdr-plugin-dvd

I can probably provide a more exhaustive list if needed.

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Migrated from T1493 (view on Phabricator)