The weirdest thing just happened. Yesterday, after casual vBulletin maintenance (username, stats and counter) I thought things were fine. As I found out now, they were.
First thing this morning member Steve-Hostirian messaged me about missing posts from 17th and 18th of April. After looking further into the issue I noticed that indeed a couple of hundred posts vanished (made after 5.50 PM of April 17) till 19th evening, along with 12 user registrations.
It turned out to be a drive issue with our hosting provider. After contacting them today within 30 minutes they moved us to another server and restored the latest backup available from yesterday night.
So everything is back to normal, registrations are back, posts are restored as well, except the few posts that were made this morning and early afternoon. I do apologize for this and to those that won't see a couple of their latest posts our there.