Red dots

[Mauro5DC1]

With Lightroom red dots are formed on the white areas such as exposure correction or whatever.

[Rob_Cullen]

The Red spots would be Clipping indicators. (Red=White. Blue=Black)

Press keyboard [J] to toggle on/off both the White and Black clipping indicators.  In Lightroom-Classic (and old Perpetual versions) you can also click on the indicator triangles on the Histogram.

In Lightroom-Desktop v4.2 the keyboard [J] toggles Clipping indicators-