Individual ticket start booking date not updated

I made some modifications on single events created through recurring events.

I changed the starting date for booking on all the events. In WordPress backend, all was fine, but on the database these modifications didn’t take effect.
I asked my web hosting company to have a look on what is going wrong.
Do you have any ideas.
Maybe I changed too many starting booking date in one time and this made a confusion.
Do you know a way to modify these single events starting date. What I done is to open all the single events and modify the ticket where the date were wrong. One by one. Maybe this is not the way to do it.