Using softwood (pine, spruce, etc.) has its advantages and disadvantages. It’s relatively cheap and easy to work with, which is good. It also has defects and knots, which is not so good, especially if the knots are coming loose. One solution is to cut the board to get rid of the loose knot but this is not always the most economical approach.

When the only issue is one of structure, and not appearance, I do a fix that will secure the knot quick and easy:

I use my biscuit joiner to cut a slot and glue in a biscuit.

After the glue is dry, I plane them flush with the surface of the board:

Works every time.