I’ve read every tip I can find on this problem, and none of them fix it. The most common one is to claim that if using a laptop (which I am) you must have inadvertently brushed the touchpad and accidentally moved the cursor that way. I have done very careful tests in which I make sure my hands never touch the touchpad while typing, and it still happens. I start to type a sentence, then pause. I can see my cursor blinking right where I stopped typing. I then resume typing, only to see nothing happening where I left the cursor, and after searching around the document I find that it has for no reason jumped to a random spot in the document and all of my new text is appearing there.
This happens frequently, many times each day, and I have experienced it over the years in many different revisions of Word and on completely different computers, including both desktops and laptops. It’s absolutely maddening, but Microsoft just never fixes it.
Many Android apps feature that sort of annoyance also.