Brother MFC-J4420DW not scanning properly

Since upgrading to Monterey on an M1 laptop the above scanner isn't working properly (I have installed Brother's latest scan driver). After struggling with Preview I used Image Capture. Using the document feeder I can scan to pdf OK, also multipage documents. But using the flatbed only works intermittently. The overview scan works OK, but the actual scan hangs at the end, at the point in Preview when it would update the combined pages document, and in Image Capture when it would show the little window that shows the pdf file. You have to quit Image capture and relaunch, re-overview scan and then rescan and it might work - I reckon about 50% of the time or less.

Any ideas how I can fix this rather vital feature for any user?