The yellow warning triangle set on a production work order (PWO) is an indication that there is not enough materials/parts to produce the product. 

A negative material trend is set on production work orders (PWO's) when access to the material and/or parts for the production work order (PWO) has worsened.

That can happen if - for example - the product is linked from goods in stock in the warehouse to a pending link, an order confirmation is received from the supplier with later confirmed delivery time, sub-production work orders (PWO's) are reconfirmed to later dates etc...

To find the productions work orders (PWO's) with this flag set, you can enter the in the  application under the 'Productions' folder:

Check off in the radio-button for 'Negative material Trend only' - and the list will show the production work orders (PWO's)  where this flag is set. 

It is possible to check out the specific production work order (PWO) and clear this flag on the production work order (PWO) if the user confirms it is ok: