Is the tubing your trying to flair metric?
good question
SUGGESTION: You might some scrap pieces of scrap and see if the problem persists.
The only time I've had trouble with steel tubing is when the flaring tool teeth were full of debris. Cleaning with a small stiff wire brush usually fix's the issue.
If the tube has been "scraped enough" you may have to cut a short piece off for a good grip.
only other thing I can think of is you might have gotten an extremely hard piece of tubing (unlikely) or the tool itself is tweaked.
keep us posted