I've had that happen with new Starline .38 Special brass, and others have experienced the same issue. The brass has to be lubricated, since bare brass sticks, rather than slides. I solved the problem by tumbling the new brass prior to the first loading, which imparted some lube (dust, media, or whatever) to the inside of the cases.
I stuck several before I figured out the problem, even changing dies. I stuck them on Lyman, RCBS and CH expanders, but after tumbling them, I never stuck another one. I had two of the cases pull in half, leaving the top half of the case stuck on the expander, and about 20 cases were stretched to the point they were ruined, as I could see where they nearly separated when pulled from the expander die under great pressure.
The way I got the stuck half off the expander was taking a Dremel Tool, with a cut off wheel, and very gently cut a groove along the side of the case, from the case mouth down to the end of the expander. You don't want to go all the way through the case and mess up the expander. You just want to get the brass thin enough to release the tension, and once that's done, it will slip right off.
You may have brass galled onto the expander, too. Once you get it cleared, you might have to polish any stuck brass particles off the expander.
Hope this helps.
Fred