Without sight of your data and model I can't say for certain, but there are three possible issues to look at.
1. Trapping - have you used wildcard or literal traps for the new fields?
2. Is the correct template set as the Detail?
3. Is there a default filter set which is excluding all the new data?
In addition to Olly's points ....
Have you checked that nothing has changed on the report between the example for which you redeveloped and tested the new model and the reports you are now receiving?
Have you checked whether the reports being sent through are as consistent as you are used to before the reports was changed? (Especially if the reports are sourced from PDF files or similar.)
Good to hear you found the problem.
In my experience one can never trust a developer to make a simple change when there are a few other things they might do "whilst we have the code open ...."
This is especially true for reports.
It's always good to assume other changes have been applied.and be pleasantly surprised if it turns out they haven't.