I am having exactly the same issue as an older, closed discussion from a couple of years ago by Michael Spiegelman
Using Quicken 7.3.2 on MacOS 12.8.
I have investment accounts (Brokerage type). I manually enter a Dividend or Capital Gains transaction. I type in the amount, hit tab, then type in the number of shares. Then hit "enter" to save the transaction. The number of shares is erroneously recorded as "0" (at least the amount is correct though).
I reopen the transaction, type in the number of shares again (swearing to myself) and hit "enter". Now the number of shares is recorded correctly.
I think this has been happening for me for the last 5 or so versions of Quicken. It does not always happen, but it quite common. It happens in all of my investment accounts!
Needless to say, this is not a great experience.