Worse Last-Time-Buy??

Hi Everyone.

We are using over 1000 NET+50 Arm processors a year for a industrial solution. We have bought over 4000 processors in the last-time-buy of last year June. These items are all having production code 0916 printed on. With this particular series we are running into what is looked like as temperature problems. We never had to apply any heatsinks on this component but now it looks like that we have to. Batches of this NET+50 Arm processors with older date codes on it are more robust to our ambient temperatures. Normally, the ambient temperature is not going higher then 50 degrees, with no problems at all. But now the processor fails to communicate on the CAN bus we programmed. We applied some FBGA heatsinks and the porcessor failed when the temperature measured on the heatsink is only just 42 degrees celsius. The rest of the board is produced with the same components, no changes are made here. Even our software has had no changes!!

Any one with the same failures, or anyone with a good cooling solution?