Did something change with the billable time. We use this feature on our invoices as “Billable time -invoiced” .
Normally we could see all of these transactions in the left column under “Billable Time”. This column however is empty now.
Are we doing something wrong?
Not necessarily - but with the little information you have provided, it is impossible to say
What edition and version of Manager are you using?
A few screen shots would not go amiss, so that we can offer more targeted advice 
Is the entire column of tabs empty? Or is Billable Time missing? Or is the tab present but shows zero transactions? And is the tab enabled in Customize?