Since 3 months client portal was working fine suddenly due to some network problem we restarted SharePoint server, after that some Active directory users complained system was inaccessible, where after checking we found previously existing users where strangely not present in share point group, sadly audit log report was not enabled so we could not figure out what happened.
My question is:
1- Is it SharePoint 2010 bug ?
2- Is problem could be from Active directory ?
3- Any user have manually performed this action, though usually they don't access server ?
Now client is asking report why this happened and we are clueless ..any help will be highly appreciated...