I have an issue with the template Expert and the display of the logo on mobile devices. It always appear at the wrong place when you scroll down for an unknown reason. Possible to check www.plagejdlm.com and explain me how to correct this issue? Pretty sure I did something wrong but can't figure out what it is.

Hello,
you did nothing wrong, but you logo is too big for a small screen size.
But you can add some css code to your css/custom.css to fix it

.uk-navbar-center {
max-width: 90%;
}