Empty tables with the new Heron Layout Model

### Bug

With docling version 2.50.0, a few complex tables are empty in the parsing results.

The tables are well detected, with proper bbox, but the content is empty (no cell, export to dataframe empty).

### Steps to reproduce

Unfortunately, I can't share the table on which it is bugging. I will try to give a pdf soon but hope I am not alone flagging this problem.

### Docling version

```
Docling version: 2.50.0
Docling Core version: 2.47.0
Docling IBM Models version: 3.9.1
Docling Parse version: 4.2.3
Python: cpython-313 (3.13.5)
Platform: Linux-6.8.0-79-generic-x86_64-with-glibc2.35
```

### Python version

3.13

Not platform dependent, problem occurred on MacOS and Linux