Pixelation in black and white images

I now think I downloaded this from my Google picture library, it had been uploaded as a NEF file automatically when I saved it onto my tablet. I need to import the original file into lightroom classic on to my computer at home and review the image quality from there. There is definitely an issue with the profile browser black and white settings. There doesn't seem to be a problem when I convert the file directly to black and white and adjust it from there. I appreciate your comments. Looks like I've got to be a bit more diligent in noting the procedure I use. It's a learning curve.

I initially used the profile browser in lightroom and this seems to be the issue. The image was saved as a JPEG, but you can still see the the problem in lightroom. I have since tried converting the image clicking on the treatment option and the result is much better. The original RAW file had been uploaded to the mobile version of lightroom and then downloaded to my computer at work. I've attached a screenshot of another image which is even worse. I realise this is a forum for photoshop, but I couldn't find another group specifically dedicated to lightroom, so a layers panel shot is not relevant. Thanks for your reply. Any insight from this screenshot would be appreciated.