Hi Alex,

from which to which 15.5.* Version are you Upgrading?

Have you Updated the Required Software on the Server?

https://www.soti.net/mc/help/v15.5/en/setup/installing/system_requirements.html?hl=system%2Crequirements

As mentioned in another post, this happened to me quite a few times, the resolution we found was to first uninstall the old version on the app-server and then install the "Update".

When just installing the new version whilst the previous version was still on the system, the deployment server kept crashing every time.