Permalinks not saving %postname%, only ?te%postname%

Hi,
i’m in a big trouble with my permalinks.

I’ve always used them as only /%postname%/ but suddenly, and without any action by my me, they changed to the /%year%/%monthnum%/%day%/%postname%/ structure.

When I try change that in my admin panel, minutes after they change back to /%year%/%monthnum%/%day%/%postname%/ without any explanation.

I’ve tried to deactivate all plugins, but still got the problem.
I also tried to change the permalink structure direct in the database via phpMyAdmin, but it changed back to /%year%/%monthnum%/%day%/%postname%/.

For me its a VERY strange issue.

Oh, my host is BlueHost optimized for WordPress (https://www.bluehost.com/managed-wordpress-hosting)

I would be glad with any help.
(and sorry about my english, I’m not native speaker)