SUMMARY

There are missing directories in the repository. You can't install the affected packages. I have found two missing directories affecting many packages.
- https://origin.archive.neon.kde.org/user/lts/pool/main/libv
- https://origin.archive.neon.kde.org/user/lts/pool/main/libq

STEPS TO REPRODUCE
1. apt sources: deb [arch=amd64] http://archive.neon.kde.org/user/lts bionic main
2. sudo pkcon install libvncclient1
2b. sudo pkcon install libqapt3

OBSERVED RESULT

E: http://archive.neon.kde.org/user/lts bionic/main amd64 libvncclient1 amd64 0.9.12+dfsg-7+18.04+bionic+build1 is not (yet) available (404  Not Found [IP: 185.93.3.16 80])

EXPECTED RESULT

Package installed


SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: KDE neon Plasma LTS Edition 5.18

ADDITIONAL INFORMATION

Two examples of missing deb files in the repository. I have checked the url of the deb package in the repository index (archive.neon.kde.org/user/lts/dists/bionic/main/binary-amd64/Packages).

libvncclient1
package url: http://archive.neon.kde.org/user/lts/pool/main/libv/libvncserver/libvncclient1_0.9.12+dfsg-7+18.04+bionic+build1_amd64.deb
problem: the whole pool/main/libv directory is missing

libqapt3
package url: http://archive.neon.kde.org/user/lts/pool/main/libq/libqapt/libqapt3_3.0.5-0xneon+18.04+bionic+build6_amd64.deb
problem: the whole pool/main/libq directory is missing