My Word randomly capitalizes the letter "i" at the start of words, how do I get it to stop

Office 2016 (365)

Thank you. It doesn't matter what document my Vice Director is in.

Whatever document she chooses to enter it randomly capitalizes the letter i at the start of the word.

I'm sorry to see more are affected by this, but still need a solution for this

I do not know if you already know why, but it is because the pronoun I should always be capitalized and word does it for you.

SIDE RANT, not directly related to the main topic

I've found this kind of response to be really common here. I post occasionally because I do sometimes get helpful answers to questions. But what I also get, 100% reliably, a minimum of once per thread I start, is people answering a different question than I asked, suggesting things I clearly state I've already tried, or otherwise posting seemingly to show off their lack of reading comprehension skills.

Often, these posts are worded in a really condescending way or assume incredibly basic misunderstandings on my part, too. Often I am "corrected" on concepts I demonstrate a better understanding of than the person responding, right in the post they're supposedly replying to. Which this is also an example of, maybe the most vivid one I've seen yet (though in this case I'm not the one directly on the receiving end).

When I've pointed this out before, people are usually like "well this is a free service and the people who answer aren't paid to be here or connected to Microsoft". But that's just as true on Reddit, it's just as true on various other tech forums I go to, it was just as true on Usenet back in the day. And while this would occasionally happen in those places too, it was rare and frowned upon, not common and seemingly accepted. None of them had this issue to anywhere near the degree that answers.microsoft.com does. And when it did happen, you certainly didn't see people jumping in to defend it!

I don't know what it is about this forum that makes replies like this so common here relative to other places, but it's obnoxious and I wish it would stop, or at least slow to the same trickle you get elsewhere.

It was pressing the Enter key at the end of the previous line that was being suggested.  If that was done, and the word that starts with i is the first word on the new line, then Word will treat it as the beginning of a new paragraph\sentence and if, under File>Options>Proofing>AutoCorrect Options>AutoCorrect, you have a check mark in the box for Capitalize first letter of sentences, that is what will be done with the I.

That should not however happen if you are typing

I was walking In the park, where I met my friend John Inside the café

all on one line.  Is that really happening?

Go to File, then Options (at the bottom) then pick Proofing on the left.

See the screenshots below...Good luck!

Changing the font is what solved this problem for me. I suspect it could be to do with the mixed Mac/PC environment I was working in with some incompatibility on the PC with a font introduced on a Mac, or vice versa.

I was also frustrated by people telling me this fault could not be related to fonts because of <insert some technical explanation>. Changing the font solved it. Nothing else did. It's not for the users to explain why!