Extremely broken lighting 1.14

We recently updated our 1.13 server to 1.14,  for several days the lighting was fine, until today when I logged on to find half my base completely unlit.  As you can see in the screenshots.  the torches are illuminating the block they sit on, and none of the rest (mostly grass).  Im guessing its not simply a client issues as the areas were completely full of mobs.  Debug screen shows affected areas have both server and client light level of 0. Not sure if its relevant but the areas affected are not exposed to sky light. Re-logging does not fix it, but placing and breaking torches fixes the immediate surrounding area.  Affected areas appear to be aligned to chunk boundaries