The upgrade has finished but with a twist, what was supposed to be an upgrade to v2.6.3 ended up being an upgrade to v2.6.4 :)
Version 2.6.4 was just a small fix https://github.com/tootsuite/mastodon/releases/tag/v2.6.4 that was introduced a couple of hours ago when I was getting ready to start the upgrade. So, I decided to wait and do the move straight to 2.6.4
All instances have been upgraded. Any issues, please let me know.