Hi @Jan_dM -
Initially I have had very good success with Particle Doctor, but the last couple of times I have been experiencing some errors as well. Usually my advice would be “If is ain’t broken, don’t try to fix it”… but it if it for a product going to a client, I would want to make sure the firmware on there is stable and done cause problems going forward.
Refer to this post. It will give you instructions on how to manually flash your boot-loader and system files via USB. You can download the latest files form this link
Also, you might want to try the following before manually flashing all the system files, it usually resolves the problem. Put the Device in DFU mode, connect via USB and run the following command
particle update -v
Hope this helps.
Friedl.