I have been flashing images that I create from the firmware selector, especially if I need to add extra packages.
If I change a config, I edit the backup and re-upload it in whole.
This is the only means I don't have corruptions, loose WiFi, etc.
I've only been able to use a WD N750 with version 21 and above with minimal configs and no added packages. Version 19 was version that didn't present these kinds of issues.
Hope this helps.
Reference of a few issues in different threads: https://forum.openwrt.org/search?q=n750%20%40lleachii%20order%3Alatest