This is not at all normal, and chances are the problem has been there for a long time, and it wasn't caused by a small change in the truss rod. Either you didn't notice it earlier, or a little change in the truss rod acted like the proverbial last straw. The root cause is a construction defect, something went wrong when the neck was built, either in materials or handiwork. If something like this happens to a guitar which is still under warranty, it's a clear case for replacement or full repairs.
In any case, unfortunately, some major repairs are going to be needed, and they're not going to be cheap. The fretboard will have to be taken out from the neck, truss rod checked, parts cleaned up and sanded down, cracks filled up, and then the fretboard will be glued back to the neck properly. Alternatively, it may cost less to buy a new neck.
Perhaps an attempt can be made at a quick-and-dirty fix, i.e. put some glue in there and keep the fretboard pressed hard on the neck until settled. As I said, quick-and-dirty. But it may be worth a shot if the guitar's value isn't too much and it doesn't make sense to spend a lot of money on repairs.
And if you don't do anything, I reckon that there's no telling of how the problem may evolve. It's possible that nothing else will happen. If there was a gap in the surfaces at that point, or glue was applied badly at that point, but everywhere else things are OK, you may still be fine, it's possible that things won't get any worse, and if the crack is felt during playing, a little wood filler can fix. On the other hand, if the underlying damage is more extensive, the crack may get worse, maybe a little, maybe a lot. That's impossible to know without knowing what's going on inside.
If the instrument were mine, and if it were not very expensive to start with, I'd do nothing at first, but keep a close look all the time, and if the crack expanded by even a millimeter, I'd take the strings off, loosen the truss rod, and take it to a pro. I the crack didn't change at all for a long time, I might decide to let it be. On the other hand, if the guitar was valuable, I'd take it to a pro right away.
