I fixed now for the 2nd time the online time and registered date. While I did this already once, there was an older process that ran on the table that reset the data. I used the other process to track username changes and did not anticipate that it would delete existing data.
The fallout is that user online time since the upgrade is lost, but we should be calculating correctly from now on. Please let me know ASAP if you see any suspicious data in this aspect.