Can't convert old outlook files to pdf - keeps 'skipping'?

I am trying to convert a large number of emails to pdf using the standard Adobe DC plug in.  This works absolutely fine with 'newer' emails but it then won't convert anything before a certain point in time (can't be certain what that point is but possibly anything older than16 months), and simply skips and fails to convert

Can anyone help with how to avoid this?

I can use the micrsoft print to pdf function without any problem, but I need to do a straight adobe conversion so that it also includes the attachments

Thanks in advance