Praxischeck.
The Migration work fine for some experienced user. Problem is aas often the software. But since SUSE Hub we have made a HUGE step ahead! A lot of problems from past is solved.
These are my experiences and tips.
Migration 12.2 to 12.3
https://www.suse.com/documentation/sled-12/book_sle_deployment/data/sec_update_migr_zypper_onlinemigr.html
follow this description. Migration as such works fine.
After Migration
Change libav  repository to packmann
For software that got broken:
For shutter:
https://software.opensuse.org/package/perl-Goo-Canvas
For FreeCad:
https://software.opensuse.org/download.html?project=home%3Aecsos&package=python-pyside
VLC
is totally broken and need to be repaired manually.
Actual, following other repsoitories are included and set on priority 100 (means, SUSE will take own respositories first. If not available, others will be used)
Opensuse Leap 42.3
Packman
After Online Update of system:
Update demands vendor change. This works, unless for VLC. Here, the vendor need to be demanded back to packman. (update VLC manually in YAST to packmann
http://packman.links2linux.org/package/vlc