All of my 30 Odroid-C2 get "Bestätigungsfehler" and 0 Points with the v4.24 app.
And no cpu-hours for all running projects counted.
With v4.19 app it worked without problem.

<core_client_version>7.7.0</core_client_version>
<![CDATA[
<stderr_txt>
14:30:46 (13926): initialisation
20:29:52 (13926): called boinc_finish

</stderr_txt>

One of the hosts:
http://wuprop.boinc-af.org/show_host_detail.php?hostid=144980

From the change of app :
data_collect_v4_4.19_arm-unknown-linux-gnueabihf__nci
to
data_collect_v4_4.24_aarch64-unknown-linux-gnu__nci

the app is ignoring app_config.xml settings, including <cmdline> section.
So we cannot run multiple instances, one per core, in Ubuntu SBCs as we used to do from serveral years. I run latest ARMBIAN in pine64-rock64, nanoPi Fire3 and orangePiPc2 / orangePiLite2

The problem is only with all my Odroid-C2 with Ubuntu 16.04 and Boinc 7.7.0.
The Odroid-N2 and -C4 with newer Linux and Boinc has no problem.

Now i changed on all Odroid-C2 from Boinc 7.7.0 to Boinc 7.17.0 and the problem has gone. All works without error.

The problem is only with all my Odroid-C2 with Ubuntu 16.04 and Boinc 7.7.0.
The Odroid-N2 and -C4 with newer Linux and Boinc has no problem.

Now i changed on all Odroid-C2 from Boinc 7.7.0 to Boinc 7.17.0 and the problem has gone. All works without error.

You do still have some older Boinc versions on some of your machines.