https://greglewisinfo.com/2020/04/18/the-b-17-saved-by-a-miracle/

The ultimate source appears to be a guy’s memoirs:

I came across this story in Elmer Bendiner’s marvellous 1980 memoir, The Fall of the Fortresses, while researching the lives of USAAF crews flying out of England during WW2.

I’m still very sceptical. This guy is not even the primary source actually:

Bohn said the shells had been sent to the armorers to be defused but had then been rushed away by an intelligence officer.

Bohn had tracked down the officer and had hounded him until eventually he had told Bohn the full story – before swearing him to secrecy.

Now, sabotage like this undoubtedly happened, although the scale is impossible to verify. However I think this specific story has just way too flimsy a chain of evidence to put any faith in. Good story though.