Hi Miljan,
A number of our users have submitted reports to us recently regarding this exact problem with the editor in the new Post and Page Builder update and our developers are currently working on a fix for it.
Adding a number of extra buttons to the editor, such as from contact form or shortcode plugins, is causing the button display to collapse on itself just like in the screenshot you provided. The fix for this issue is currently in the testing phase and we hope to get it released very soon.
In the meantime, you can restore the normal editing experience by rolling your Post and Page Builder installation back to a previous version by using the WP Rollback plugin from the WordPress community.
Thank you for your patience while we work on getting this fix released and please let us know if you have any additional questions for us!