The accuracy of GPS is somewhere in the 3 to 15 meter range, depending on the quality of the fix. Once you slow down, the jumpiness is the fix moving around inside that range from fix to fix. Static Navigation turns off any small movements so that the jumpiness goes away, which is good, but it also means you aren't really navigating any more. Depending on how your receiver is designed, you would have to resume movement above the threshold (usually 2-3 mph) or move greater that the threshold distance from the last fix (usually about 20 m). I can't tell you how to set Static navigation on your unit, but you can look at the manual
here. From a quick search, it doesn't seem to have a setting for that. Beeline doesn't ignore any fixes, so I don't think you can avoid the jumpiness there.