There is a browser bug that causes your logo to get a 0 pixel height when using an SVG image so when you upload an SVG image it may seem like it’s not working but really the logo is on the page but with a 0px height. To fix this, simply add a little Custom CSS to your site to give your logo a fixed height. Example:
body #site-logo a {
height: 50px;
}
body #site-logo img {
height: 50px;
max-height: 50px;
display: inline;
}
body #site-logo,
body #site-logo-inner {
display: block !important;
height: 50px;
}