This could be a number of things.

The first could be simply due to the time of testing relative to the last injection being different from the last test.

The second & what is potentially likely here based on what you've said; Lowering body fat helps to lower Estrogen. Estrogen is fat soluble & overall having less of it also helps decrease it. This is why there can be a negative feedback loop for men not on TRT where they gain weight & increase Estrogen & now it is harder to lose that weight because the ratio of Testosterone to Estrogen has changed.

To a lesser degree muscle mass & resistance training can increase Testosterone. When dieting, unless you're a world class body builder you almost certainly lose muscle as well, there could be a drop from that. However once your hard dieting is over & you return to less stressful eating/muscle gaining situations, this would probably change back for the better. Diets are stressful on the body overall & can have side effects.

This is all some conjecture based on what you've said, but I hope it helps. I wouldn't worry about it unless it continues after your diet ends or increases.