Everyone Hates iPhone Autocorrect. An Update Fixes One of the Biggest Problems
wsj.com
wsj.com
I've described this better in another comment which has a better video of the problem in the related article: https://news.ycombinator.com/item?id=46242496
It might help if you take a slo-mo video from a second phone showing the users finger movements on the screen. Unfortunately the touch point is a lot finer than the finger pad, so it still wouldn't be clear.
On Android there is a dev feature to show touch points which helps debug people's mistakes (and has the advantage of showing the actual touch points sent by the hardware on video of screen capture). On iOS maybe similar feature in some custom keyboard Apps (or configuration choices?).
The other issue I often have is repeated words. I’ll type a word once, but auto-complete will also throw it in there.
I don’t think either of these are sliding issues. I tried manufacturing a slide to see what it would do and had a lot of trouble making it do anything that would replicate the typical errors I run into. Most of the time it tried to start swipe typing. If there was a delay it could start sliding on accents. When I did get it to pick the second letter, it started throwing in extra spaces and acting pretty odd.