I have a model 34 from my grandfather.
It sounds like somebody replaced the magazine spring tube with one from another gun. The model 34 takes a long follower on the end of the spring, a short follower will load all the rounds except the last one correctly.
You can order a new spring tube with a long follower from Brownells.
I have an extra here,, but it has the short follower that I accidentlly bought for another gun with the same problem...
If it is the right spring , spring tube, and follower, then the spring may be weak, or there is a crimp in the tube that is not letting the follwer come all the way out... Or it is full of old hard grease and grit....