As a follow up to {T164617}Thanks to help from @Milimetric, the issue was narrowed down to be present only on FF/Safari on Mac.
1. Log in to deployment-eventlogging03:/srv/log/eventlogging
2. To track/count of click events - RecentChangesTopLinks, I used `grep RecentChangesTopLinks all-events.log |wc` and `tail -f all-events.log | grep RecentChangesTopLinks`
3. On RC page click on any top links (blue ones) - first two clicks will be counted (doesn't matter if the same link was clicked twice or separate links were clicked). Subsequent clicks will be ignored.
Logging click events needs more investigation
- the same user for whom clicks are stopped being recorded, can log in from a different computer and clicks will be recorded again
- a different user with the same IP will have two first clicks recorded
- clicks from mobile devices won't be recorded