Stock correction issue in 15.0.3

I have several instances whereby when I add (increase) the stock for stock correction, the system instead of adding the stock to the quantity, the quantity get deleted (reduced) accordingly. This is not a consistent occurrence. Sometimes it works as expected. I am very sure I choose the “Increase” instead of “decrease” option in the stock correction. The version that we are using is 15.0.3. This happens not in just one instance, but over multiple days for now - hence I suspect it’s not just a one-off glitch in caching/browser related. I wonder if there is anyone out there have similar experience? Any suggestion is much appreciated. Thanks in advance.