Dense numeric tables. A model reading a financial statement image can transpose a digit or drift a column, and the output looks entirely plausible. For anything where the number must be right, extract with a purpose-built pipeline and use the model to check for consistency rather than as the source. This is one of the most common expensive mistakes in document AI.
Small text and poor scans. Accuracy degrades with resolution in ways that are not signalled in the output. The model does not say “this was blurry”; it produces its best guess with the same confidence as everything else. Image quality checks belong before the model, not after.
Precise spatial or dimensional reasoning. Reading a technical drawing to summarise it is achievable. Reading it to extract a tolerance you will manufacture to is not, and should not be attempted without verification.
Counting. Counting objects in an image is unreliable at anything beyond small numbers, and it fails silently. If a count matters, use a detection model built for it.