weird issue after updating joomla to 3.8.7

[vieuxcampus]

I'm facing a weird issue after a joomla update to 3.8.7.
It's impossible to change anything in the shopper information tab. If I change the user name it comes back to a user name, always the same, which is not the one I entered.
But worst of all: If I change the email in the email input box, the credentials for the super admin are changed and it's impossible to login to my site. In this case I have to go to the database to go back to the previuous credentials.
joomla 3.8.7
php 7
virtuemart 3.2.14
thanks for help
regards