Application and database design that allows users to enter bad data. The users are (generally) not to blame, they will take the path of least resistance, and we end up with bad data that needs addressing.

I work in the NHS, and often some requirement will arise that the hospital's Patient Administration System (PAS) can't properly handle, so a workaround is required. For example, I work at hospital A, and hospital B decides to use our spare capacity to do some of their clinical work - our PAS has to record this activity, usually by storing some identifying data in a data item not designed for that purpose. Which ultimately means the data warehouse receives data for a different hospital, which then needs to be stripped out of all operational datasets etc. But, we have to ensure that hospital B can see that data (this can mean various things from direct to indirect access) so they can receive payment for it.

These are regular challenges and at a high level they haven't changed much over the years, although technology changes have occurred, e.g. HL7 interfacing (and interfacing in general) is a much bigger part of the work than it was 10 years ago.