I'm not sure what you had it up on, but don't use the ratchet style jackstands, cuz they can get bumped off the ratchets & drop - so only use the pin style, & try to place them at the 4 jacking doughnuts, or else use vee-notched 2x4 wood at the other seams/etc. jacking points as shown in the pic in the 914info section at the top of the page.
If that wheel/caster & bit of red framing showing was a 4-post wheeled cart supporting the car at those jack points, then it looks like the welds or angle-iron may have failed, which means it was either defective, or undersized for the weight of the car.
In either case - get better jack stands or cart supports before you do anything under there!
Also, that nudging before crawling under is always a good safety check!
Be Safe!
Tom
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