This should be JavaScript overriding or interfere issue.
Most likely caused by third party plugins..
Disable all the plugins except these default plugins : https://www.8theme.com/documentation/xstore/plugins/included-plugins/ and check this.
if you do not see the issue try to reactivate the plugins one by one and find the problem caused plugin then contact their support for this.
if you still persist the issue let us know your wp-admin login details and FTP details to check this.