I’ve been swapping cranks recently just to see what different lengths feel like. I put my Moment 150s back on my KH 24 last week and since then have ridden 56 miles. Yesterday my left pedal stroke felt a little strange so I rode four miles home and this morning checked the pedals and tightened the crank bolts before taking the uni out - the crank bolts were tight and just pinched up an eighth of an allen key turn.
Got on the uni and rode about two miles before getting that loose pedal feeling and then before much further the left crank fell off.
The thread on the crank bolt looks a little the worse for wear, but I wouldn’t say it was stripped. All very starnge to think I could do 56 miles, tighten the cranks a pinch and then two miles later one of the bolts has completely unscrewed itself!