You are pinching the bar.

The chain gets stuck because the wood closes in on the bar. That is almost always the cause.

The wood pinches when the cut closes up behind the saw. This happens when you cut a branch under tension—it bends, pinching the bar right as you finish. Or when you cut a log that is resting on the ground but not supported evenly. The weight of the log squeezes the cut shut.

Another common one: you cut too deep without accounting for where the weight is. A log on the ground, you cut from the top most of the way, then flip it and cut from the bottom to meet the first cut. If you try to cut all the way through from the top, the log settles and pinches.

Bucking on a slope can do it too, if the log rolls and traps the bar.

There is also the dull-chain problem. A dull chain does not self-feed—you push harder, the saw rocks in the cut, and the chain binds. But that is more about getting stuck in a bind than the wood squeezing it.

The fix: plan your cuts so the kerf opens, not closes. Use wedges on big logs. Cut the tension side first on a bent branch. And never force a saw that is stuck—shut it off, wedge the cut open, and pull the bar out.