Hi perhaps the filepath where you placed the SDK is too long? Are you using Windows? There has been many cases in Devzone about this problem, for example see here.
You can try to shorten the path name where the peripheral_lbs sample is located, it's recommended that the ncs folder is placed right under C:/
One thing you should know, the PDK is deprecated and is no supported in NCS v1.5.1. I recommend to get a production-level nRF5340 DK.
The latest release of NCS that has support for the PDK is v1.4, so you can try downgrading your NCS version, but at the end of the day the chip in the PDK is only an engineering version and not supported for production so I strongly advise you to get a nRF53 PK as soon as possible for continue development in the nRF53 platform.
