Could be Reynaud’s (but might not be).
Sounds quite like mine which is ‘classic’ primary Reynaud’s with low temperatures causing top two joints of fingers to go blue and stiff then white and numb. The vibrations caused by riding off road seem to make my symptoms worse at times regardless of temperature.
As said above, can make riding difficult/dangerous when fingers stop feeling and/or working mid-ride.
For me glove liners didn’t help much. I try to make sure my hands are proper warm before winter riding and stop and shake them out for 5 minutes if I feel them stiffening up (best trailside remedy I’ve found – I also carry chemical hand warmers with me as a last resort).