Is the Issue only with column headers or with column data as well?Does this happen across many reports?
Try creating new report tab and drag the three fields into display, to see if it shows correctly on new report of exiting document.
If its an issue with only column headers, you can simply switch to static header text and further check if the formula used in column header is wrongly pointing to different object.(i.e Name(objectA) for object B etc)
Also, check if you are getting any partial results warning on the report, If so ensure you uncheck the "Limit the result to rows"on query properties
Thanks
Mallik