[Bug 1895469] [NEW] KDE Connect constantly loses pairing, can't share/receive files

[Ascaris]

Public bug reported:

When I pair KDE Connect with another PC running KDE connect, the pairing
works as expected, and some of the functions work. Most of them are not
useful to me, connecting PC to PC rather than PC to phone, so I only
really use the shared clipboard and file sharing, and ping for testing.
Ping and shared clipboard work, but files cannot be sent (using "share")
in either direction. The "receiving file" dialog appears on the
receiving PC, but it never progresses. It does not work from the KDE
Connect tray menu or from the command line either.

The pairing is not persistent either. When the PCs are paired, pressing
the "refresh" button in the KDE Connect dialog causes the pairing to be
lost on both PCs, and so does rebooting.

This happens any time at least one of the paired PCs is running Kubuntu
20.04 or another Ubuntu 20.04 derivative, like KDE Neon (20.04 rebase),
or even Mint Cinnamon 20 with KDE Connect Indicator.

It doesn't matter what distro is on the other end, or which of my PCs is
the one running Kubuntu 20.04 (or if they both are). Fedora 32, Kubuntu
18.04, Neon (18.04 base), OpenSUSE Tumbleweed, and Manjaro all work with
one another as expected in all the combinations I tried. I tried it with
the PCs connected wirelessly, by ethernet, or one of each, and it was
all the same.

I even tried booting to a live session of Kubuntu 20.04 and pairing that
with a PC running a non-Ubuntu 20.04 release, and it did the same. The
issue is apparently not in any of the changes I made.

I had made a bunch of modifications to my Kubuntu 20.04 installation
previously, like grabbing the Qt and frameworks version from the Groovy
repo, so I just today reinstalled Kubuntu to use the ubuntu-bug tool
with the default packages showing.

I tried the thing in the KDE Connect troubleshooting guide to open the
necessary ports in UFW, and it didn't help, so I tried just removing UFW
(with the Kubuntu installation I had before this fresh one) as a test,
and it made no difference.

Kernel versions have no effect on any of this. I've tried 5.4 to 5.8,
Ubuntu and mainline, as well as those from the other distros I tried,
and they made no difference.

I reported this issue in KDE's bug tracker also, but it seems that the
bug originates upstream from Neon, in Ubuntu. The last iteration of Neon
that was based on 18.04 had all the same KDE package versions as the
20.04 version that replaced it, yet Neon (18.04)'s combination of KDE
Connect 1.4.0, Qt 5.14.2, frameworks 5.72(?), etc., worked fine, while
the 20.04 version of Neon worked the same as Kubuntu 20.04, which is to
say, badly.

The report from ubuntu-bug should be attached.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: kdeconnect 1.4-0ubuntu5
ProcVersionSignature: Ubuntu 5.4.0-47.51-generic 5.4.55
Uname: Linux 5.4.0-47-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu27.8
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: KDE
Date: Sun Sep 13 09:54:02 2020
InstallationDate: Installed on 2020-09-13 (0 days ago)
InstallationMedia: Kubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
SourcePackage: kdeconnect
UpgradeStatus: No upgrade log present (probably fresh install)

** Affects: kdeconnect (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug focal

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Title:
  KDE Connect constantly loses pairing, can't share/receive files

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