Help with artifact problem

In general, the image seems to be underexposed with a rather strong vignette added. After increasing the exposure, I would also set the white and black points (I used LR), as It appears those marble stones (headstones?) should be more white and not so gray. That may be improved by just improving the exposure.

Perhaps oversaturation and perhaps some vignette. That might also be a reason. It also looks a bit underexposed. You can see this in the histogram - it's weighted on the left:

This is a photo of a very beautiful garden. I like the way you captured the different features of the garden. However, it does not appear to be as vibrant as it could have. Zoom the photo to 100% and take a look at the grass area near the base of the photo. There you'll see a bluish appearance incorporated among the green of the grass. That I believe is what the moderators saw. Your photos should be sharp and vibrant, with the natural color of the subjects preserved. See the Adobe Stock Contributor Guide at tagproducts_SG_STOCK-CONTRIBUTOR_i18nKeyHelppagetitle for more guidelines. Take note of the appearance of the photos in the Guide. I hope this was helpful.

Best wishes.