thank you for your help. With your indications, I managed to see that my provider gave me randomly a Public and a private IP. I asked for them, they said that the problem wasn't at their side but magically, direclty after their email, I never experienced this switch of IP.
I enabled/disabled mobile data by sms so many times for testing only ! My goal is to connect to an industrial system several times a Year max. for security and economy reasons, stopping data is a good choice.
I don't discover the auto-reboot feature but when I read in detail your implementation, this feature will be activated soon ! thanks for that.
One more thing, I had a secondary SIM PIN blocked, I put the PUK number into the settings but with no chance (Status : SIM Error, PUK required). I needed to buy a old school Nokia to enter the PUK. all is ok now.
Is the PUK config only a screen information or does it normally unlock sim ?