Suddenly broken references (with yellow warning triangle in my data column)

[LePainDemi]

Hello, I have suddenly problems with my references. I have yellow warning triangle beside my column. One of my table has not any relations with other table (it have to)

I don't know how this happended if someone can help me please...

(My App is in French, it will be a plus if you know French)

[1minManager]

Typically means the record to which the ref column refers to now doesn't exist

[LePainDemi]

When I delete the parent, the children which have the parent as REF should be deleted as well. But not in my case anymore (some days ago, it was working very well).