I don't have definitive answers here, only a thought. My weight loss surgeon had us get complete lab work, including nutritional labs, quite regularly. I believe it was at 6 weeks, 3 months, 6 months, 9 months, 12 months, 18 months, 2 years and every year thereafter. I am not sure how often other physicians recommend this.
I would definitely discuss the results with your weight loss surgeon. Some changes are typical in WLS patients and may not be indicative of an ongoing problem.
However, I would absolutely watch the numbers and speak with the surgeon about it.
I am going to get my 4-year labs done fairly soon, and am anxious for the results. Labs have been good so far, although am trending toward anemia. Hoping the change in vitamin regimen will fix that, though.