Hello ,
09/15/19 I purchased 10 items 958-G80SC-SM-501 from Mouser and I encountered the same problem indicated in the post.
Currently I have mounted 3 and 10 units purchased in August and all 3 show the problem “STM DFU mode” while 10 MCU of a previous version, mounted on the same hardware, work correctly.
In the post there are no indications on how to solve the problem and the solution is not indicated, as indicated I contacted the supplier.
The oscillator works and windows reports the device not as USB but as “STM in DFU mode” now what should I do with these 10 MCUs?
Please email directly with proof of purchase and we will give you the needed steps to fix the use.