I use keychain secure notes to store large numbers of passwords and info securely , and also now and again suffer from keychain access blanking secure notes so that all information they contained is lost, this is a big problem with keychains, and also reduces my faith in keychains completely. My conclusion is that this is occuring when a keychain is left open in the background and times out and the keychain locks itself and then goes into some form of deep sleep, and when awoken the secure not appears to be blank or somehow is then blank.
To minimalise the chance of this occurring my theory of using keychains involves saving and closing them and not leaving them open unsaved or open or timing out and locking with unsaved edits in them, whilst the machine goes to sleep as im convinced it is in that situation the blanking is somehow occurring. this flaw is at least 5 years old in my experience and it surprises me no-one at apple has recognised or fixed this problem, I guess the real issue is to identify in what exact circumstances it is occuring.
I was personally going to switch to one password, but since that has no import ability, Im stuck in a tough place as 400 secure notes each containing many logins and information is not really feasable to translate into one password without huge time and energy and expenditure, so I also struggle along with keychain and its frailty
