Hello,
thanks for your reply.
I read all related topics for the last 4 months that looked similar to this issue:
I made different tries with the addons.config like suggested with the one mentionned above :
By removing package=“standard” line.
I still have the same issues.
I thought it could be related to an ‘old’ 4.2.1 or 4.2.0 no longer available as the logs suggested and deleted the following files before 2.5.2 installation:
userdata/config/profile.config
userdata/config/org/apache/karaf/features.config
userdata/config/org/apache/karaf/features/repos.config
userdata/etc/config.properties
userdata/etc/profile.properties
userdata/etc/startup.properties
userdata/etc/version.properties
userdata/etc/org.apache.karaf.features.cfg
userdata/etc/overrides.properties
After installation, it does not even start (no logs).
By the way, before any attempts, the userdata/cache and userdata/conf were deleted.
I am starting to be out of any ideas 
Does it mean I have to remove all my existing configuration before installation? (harsh)