Loading the metadata plist worked for me:
Turn off spotlight:
sudo mdutil -a -i off
sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist
sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist
Turn on spotlight again:
sudo mdutil -a -i on
Now everything is being reindexed as expected.
For me it was not necessary to do unload/load procedure.