As soon as I try to develop a photo changes occur in the thumbnail view but not in the loupe view, can anyone help please?
It sounds like you may have a defective monitor profile.
As troubleshooting, and as a possible temporary fix, try setting the monitor profile to sRGB.
If this fixes the issue, you should ideally calibrate your monitor with a hardware calibrator.
Thank you, I had been struggling with this for ages, works perfectly!