When I replaced my driver's side axle half-shaft a couple of years ago, when I first inserted the new shaft into the differential, it became stuck about half-way through the insertion. With some wedging and pounding, I was able to remove the assembly and noticed that the Circlip on the end of the shaft was of a poor quality and had large burr which had caused an interference. If I remember correctly, the Circlip groove was chamfered more than I would expect, allowing the burr to catch and to shift the Circlip out of the groove, which is why the whole thing jammed. I removed the Circlip, carefully reformed it with a hammer and file and reinstalled it on the shaft. While on the shaft I continued forming the Circlip to reduce its diameter and I used some heavy grease to make sure it remained centralized on the shaft. Everything was fine after that.

Very scary though, to have a half-shaft half-way stuck.