I changed the information in my user profile and shortly afterward clicked on (my) user activity log to see whether this action is logged. Instead of getting the activity log, the page failed to load and reported a system error. The user profile was edited several times over a span of a few minutes just before testing the activity log, though I did not have to fill out any CAPTCHA as a result.
(edit: activity log on meta can be viewed without problems, the log on the main site is the one that is broken.
edit-2: still broken after 4 hours elapsed. I will test it again in a day or two.)