Email Analysis Overview Report in Eloqua - Incorrect numbers

For an email that was delivered, the email analysis overview report shows numbers which are incorrect. Here is an example of what the numbers look like

Most contacts have been soft bounce back

Email sent number is less than unique email open

Soft bounce back contacts show up in email open report which means they have opened the email

Is there any specific reason/technical issue for this behaviour in the report.

Best,

Kamal