Assuming you posted elsewhere, but just in case...
You just have the classic issue with Italian threaded BBs. The right hand threads will work loose. It is why most of the free world has switched to the English BB standard, where the right hand threads are in the opposite direction from Italian. I had the same issue with my Colnago Masterlight. The first time it happend I didn't realize what the problem was. I was in the middle of a century ride, so it made for a fun walk.
The only thing that worked for me was teflon plumbers tape. I put several wraps on the threads to tighten it up. And I REALLY tightened it up. Went in VERY stiff, but it kept it in place. I also got in the habit of checking it regularly. Biggest thing I learned was to make sure all new bikes I have purchased were English BB.
Had the same issue, used loctite222 all over the thread and works beautifully.
Then some friends suggested it would have been impossible to remove the cup, so I tried, came off no problem, so I reinstalled with the same loctite.
Very happy and a little noise that I could hear went away in the process.
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