Upgrade of old installation

Hi,

I had to upgrade old installation of endlessos, since at one moment it stopped upgrading itself saying that there is no updates (even that in reality there was updates).
Following " Upgrade failure due to expired security key - Work around an upgrade issue on old Endless OS releases where the security key has expired" I was able to upgrade to version 3.9.7 and stuck there.
AppCenter - Updates says software is up to date.
‘‘eos-update-ctl update’’ from terminal says that there is new version 4.0.14 but during the Fetching state it exits with error:
Can’t call Apply() while in state Error (36)

Here is eos-diagnostics file got immediatelly after the error
and screen messges

would somebody advise how to rectify the problem and update to latest (possible) version of Endlessos

thank you
eos-diagnostic-250730_090138_UTC+0300.txt (1.4 MB)
screen_mesages.txt (2.0 KB)

Update:
Found in eos-diagnostics file what I think is the core of the problem

Jul 30 08:58:50 endless eos-updater[1595]: Fetch: failed to pull necessary new flatpaks for update: No such ref ‘app/org.gnome.Rhythmbox3/x86_64/stable’ in remote flathub

If I try to instal with flatpak - for example
s@endless:~$ flatpak install -v cheese
F: No installations directory in /etc/flatpak/installations.d. Skipping
F: Opening system flatpak installation at path /var/lib/flatpak
F: Opening user flatpak installation at path /sysroot/home/s/.local/share/flatpak
Looking for matches…
F: Fetching summary file for remote ‘eos-apps’
F: _flatpak_dir_fetch_remote_state_metadata_branch: Comparing 5767d84e2d11799b911b68df7c9b45263270bddf5f17747fe8b9dbeca56509b5 from summary and 5767d84e2d11799b911b68df7c9b45263270bddf5f17747fe8b9dbeca56509b5 from repo
F: Fetching summary file for remote ‘eos-runtimes’
F: Fetching summary file for remote ‘eos-sdk’
F: Failed to download optional summary: GPG signatures found, but none are in trusted keyring
F: An error was encountered searching remote ‘eos-sdk’ for ‘cheese’: Unable to load summary from remote eos-sdk: GPG signatures found, but none are in trusted keyring
F: Fetching summary file for remote ‘flathub’
F: Failed to download optional summary: URI https://dl.flathub.org/repo/summary exceeded maximum size of 10485760 bytes
F: An error was encountered searching remote ‘flathub’ for ‘cheese’: Unable to load summary from remote flathub: URI https://dl.flathub.org/repo/summary exceeded maximum size of 10485760 bytes
error: No remote refs found similar to ‘cheese’

Result is the same if try something related to remote repo flathub.
For example:
s@endless:~$ ostree remote refs -v flathub
OT: _ostree_fetcher_should_retry_request: error: 115:0 URI https://dl.flathub.org/repo/summary exceeded maximum size of 10485760 bytes, n_retries_remaining: 5
error: URI https://dl.flathub.org/repo/summary exceeded maximum size of 10485760 bytes

I suppose that this limitation interrupts fetching process during attempt to upgrade as in my previous message.
Any help appreciated

thanks