Problem upgrading via OCC-command from 10.1.0.4 to 10.2.1

Hello,
I have written myself a small step-by-step guide to manually upgrade my OC installation on my shared hosting instance. (I have no root access, so sudo commands are not possible to execute.)

Basically it follows the instructions " Upgrading ownCloud with the Updater App" from here:
https://doc.owncloud.org/server/10.1/admin_manual/maintenance/update.html

I used this script for the last 2 years or so to periodically do my upgrades. No problems.
But… following the steps here, it fails for 10.2.1… what could be the reasons?
Where there some changes recently concerning the manual updater app?

Steps to reproduce

  1. Via ssh:
    Step 1 rename owncloud folder to current-time-stamp backup
    mv owncloud/ owncloud-dirbkp_date +"%Y%m%d"/

  2. Get current release:
    wget https://download.owncloud.org/community/owncloud-10.2.1.tar.bz2

  3. Extract release into new owncloud-folder:
    tar xjf owncloud-10.2.1.tar.bz2

  4. Recover “config” and “data” from the previously taken filesystem backup:
    cp -fR owncloud-dirbkp_date +"%Y%m%d"/config/ owncloud/config/
    cp -fR owncloud-dirbkp_date +"%Y%m%d"/data/ owncloud/data/

  5. Start the manual updater app
    ./owncloud/occ upgrade

Expected behaviour

The upgrade should start.

Actual behaviour

I get an error message (red colored box)
Command “upgrade” is not defined.

Server configuration

Web server:
apache

Database:
MySql

PHP version:
7.1.30

ownCloud version: (see ownCloud admin page)

installed 1
maintenance
needsDbUpgrade
version 10.1.0.4
versionstring 10.1.0
edition Community
productname ownCloud