its definitely a deficiency that could have been avoided, but you are now a couple of weeks from the end and you will be able to finish, but it is going to be an ugly finish. No worries, we have all been here at least once.
the task now is to figure out what got you here. I oftentimes find this happens to someone who never varies the pH and always comes in at the middle of the range. Sometimes missing out on the added mobility of some of the elements at the lower part of the range, even just a few times during the grow, finally comes to bear toward late bloom.
Another thing it could be is salt lockout. This is a thing, and can oftentimes hit about now too. A good 3x flush is called for if this is the case, and a few years ago this would have been the automatic advice given on a thread such as this.