Header went from days to weeks
 

Previously I could see a date above each column.

Something has changed and I now I just see "Jan 1- Jan 7" across all columns.

How do I get Omniplan back to showing a single date above each column?

Thanks.

It sounds like you were using the day timescale in the Gantt Chart, then switched over to automatic or weekly scaling somewhere along the way. To change this you can click on the magnifying glass icon in the top-right corner of the Gantt Chart and select day scale.

Does this fix the issue for you?