The filled ones are "User" markers. It's a longstanding bug that SONAR arbitrarily inserts these on some or all beats when first enabling Audiosnap in some cases.
You can select them all and delete them. But because Delete Marker only gets one at a time, I suggest binding a key (e.g. Ctrl-Delete) to Delete Marker, so you can hold it down, and get all of them. I do this as a matter of course whenever User markers show up spontaneously.