Non existent words

I have autocorrect and auto capitalisation on my iPhone 8. In all my past iPhones I’ve had those random corrections but since an update a few months ago (I cant remember which one) I’ve had very random words. Today I typed in nothing and was autocorrected to boingg. I like the autocorrect and autocapitalisation as it’s easy for the finger to slip. But I’ve just typed finger and figg big and fi ne came up. Is there anyway to stop this happening I’ve reset thy e keyboard settings and the phone itself but nothing’s changing. I don’t mind it auto correcting words but it’s changing words to a random combinations of letters and spaces. Also I was texting someone about my grandmother yesterday and Nan keeps getting put as NaN I’m having to go back and change it every time. I’ve never wrote NaN like that on my own.