I've never seen this issue with my Brother MFC-2740DW using "Image Capture" on my Mac (which I assume you are referring to as the built-in scanner app). It's worked flawlessly for me (as did my previous Brother laser printer/scanner).
I am still using Mojave; I was unaware of the "Image Capture" app - I opened the printer icon, which has a "Scanner" button on the right when you have a multifunction printer - but it appears to be the same underlying implementation, and it has the same bug, described here:
https://support.brother.com/g/b/faqend.aspx?c=hk&lang=en&pro...
perhaps it was fixed in Catalina; the page I linked (with the exact kind of corruption I just tested through Image Capture) is from 2012...