Data Merge - Can't preview without errors
The apparently long-running Data Merge previewing error!
Occasionally previewing a data merge will permanently ruin exports. The only solution is to create a new document. Happened to me on almost every project I tried - wasted hours and hours.
See this thread and video for more information:
(Also colons in csv titles makes file unusable??)
This does waste hours, previewed early on and spent a ridiculous amount of time assuming my files weren't set up correctly when it was InDesign the whole time.