If this happened twice with the same transmission I would look inside the trans for an issue.
Did the axle slide in and out easily without the clip?
Perhaps something is binding in the spline area. My pass side axle gave me a devil of a time (86 4-spd-2.8) getting out while replacing an oil seal. The clip did not break but it was a disturbing experience.
Spoon
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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut