What is the interpretation of an IGRA with positive TB wells and negative nil and negative mitogen wells?

A patient on meloxicam for LBP developed high, persistent fevers and no other symptoms. An IGRA, among many tests, was sent. The IGRA’s mitogen well was negative (the TB and nil wells were negative as well). 8 days later, the IGRA was repeated and again, all wells, including the mitogen well, were negative.
Does the fact that her PBMC, when exposed to a mitogen, on two separate tests done 8 days apart by a large, commercial lab mean that the lab mishandled her PBMC twice or something is wrong with her cellular immune system? A patient, who was epidemiologically at risk for prior TB infection, had an IGRA prior to receiving immunosuppressive chemotherapy. The nil and mitogen wells did not produce significant amounts of IFN-γ, but her TB wells did. The lab interpreted this test as indeterminate. A follow-up test was not sent. How should this result be interpreted? Of relevance, at this time, the patient was receiving chemo, had markedly elevated WBC and fever of unknown origin.