How old is the house? If this a new home under 1 year, could be ground settlement, it could also be the footing failure if one was installed if not poor sub-base compaction... It could also be caused by rainwater if drainage along the wall wasn't installed.

Wall needs to be taken apart, footing or proper subgrade needs to be installed and compacted and the wall should be re-done.

Good luck

Thank you for the response. Yes the house is less than 1 year old. Landscaper believes it is an issue with compaction but your comment about water drainage is interesting to me. I don’t believe there is anything special installed specifically for the wall.

I've had that problem with a similar wall at my 17 year-old house. I bought the house when it was 3 years old and noticed the same issue, so I disassembled the wall, laid some gravel, compacted it, and re-stacked the wall. It was good for a while, but has been slowly subsiding again for 3-4 years. I believe it is a combination of inadequate compaction and water in that location (we get a lot of rain and subsurface movement of water in the Pacific NW). I plan to redo it again when the weather is better. I'll try further compaction followed by placing a concrete footer with rebar under it.

It's annoying that you have this issue, especially so soon after having it built, but it's not that much work to take these blocks apart and re-stack them. Good luck.