They just get worn over the years from constant take down use. The end of the tube was supposed to make some contact on the receiver when the takedown lock pin was tightened up. That made the tube a firm fit against the receiver and the large square threads kept it from wearing out too awful quickly.

But those guns are anything from 100+ yrs old to just less than 60. The sheet metal tube end has just plain worn or in some cases been rolled slightly inward from pressure aginst the receiver and allowed the tube to twist loosly in place.

There is supposed to be a slight rolled lip at the end to contain the mag follower in the tube, but too much pressure against the receiver can increase the curl to the point where it can cause feeding problems catching the shell rims.
A balancing act that opts for light pressure to avoid turning that lip inward causing feeding problems. But that allows the mag tube to loosen up after some use and rock slightly in it's locked position.

Solid frame 97s have their tube screwed into the frame with a very fine 'v' thread and held into position with a set screw on the right side of the frame. I've never seen one stripped and loose/turning free in the recv'r. But if it's not turned all the way in it can cause feeding problems as the shell rims can catch on in the slight void between the end of the tube and the receiver edge.