For diagnosis, first choice would be a structural engineer. Building surveyors "should" be able to diagnose movement, but many can't or wont because of their insurance, and like to refer you to a structural engineer ...... after they come and have a look. Unless the builder is a structural engineer in the week, then best not ask them.
But whoever comes out it will be the same old thing, check any nearby drains, check trees, check if cracking inside, recommend a trial pit investigation or fit crack gauges over it and monitor for a year.
Are there any cracks in the same place on the inside?
Have you got photos from further back? showing most of the elevation?
Five years is a long time for things not to have moved more, so it may well be that movement was a one off. But check if the cracking is widening at either the top of bottom of the the wall. You can do this yourself every three months, and if no movement for another year then move on to repair.