Hello,

I can't be certain from your photos, but scale is definitely a possible explanation for the bumps you're seeing on your stems.

This fact sheet from The Morton Arboretum provides information on various types of scale, what plants they affect and treatment options.

https://www.mortonarb.org/trees-plants/tree-and-plant-advice/help-pests/scale-insects

You might also find these alerts from Ohio State Buckeye Yard and Garden Line helpful. It's possible what you are seeing is dead females from last year, but compare the photos in the first link to confirm this. Both of these articles have several close-up photos as well as explanations which should help you ID exactly what you are dealing with.

https://bygl.osu.edu/node/1252

https://bygl.osu.edu/node/943

As noted in the above articles, hard-body scale is difficult to control because there's a narrow window when the insects are vulnerable to insecticides, but the first article also includes methods to remove them manually by scrubbing them off. It's important to get a positive ID before deciding on a treatment option because the most effective treatment is  highly dependent on the insect.

I would recommend checking all of your other fruit trees for similar issues because scale insects can have a broad host range so other trees may well be affected.

Concerning your tree flowering but not producing fruit, it's possible that it needs another year or two to reach full maturity. This article has a good overview of selecting, planting, and caring for apple trees and covers various reasons your tree may not be producing fruit.

https://ohioline.osu.edu/factsheet/hyg-1401

For further assistance getting a positive ID, you could try contacting your local extension office at https://fairfield.osu.edu/