When I'm looking at my Stack Overflow timeline according to the API, It's missing a lot of events.
According to the API, the last thing I did was posting this answer, five days ago, and you can see edits are reported as well (the second entry). However, I've made a couple of more edits since then, as you can see in my profile:
It can't be the case that actions via the API are not reported; I've made a couple of manual edits as well, e.g. this was a manual edit via the website itself.
Accessing the timeline via
/me/timeline doesn't make a difference; I get the same results. As for other sites: on Meta Stack Exchange, my last reported action is this comment but
I my script made three edits since then; some other sites, like the Russian Stack Overflow and Photography, the timeline is up-to-date.