I have one tomato bush out of about 50 plants

Internal Browning (IB), Graywall (GW) or Blotchy Ripening (BR) - A complex of disorders, hence the various common names applied, that result in irregular ripening, yellowing or internal browning of fruit. Tobacco or tomato mosaic viruses (TobMV, TomMV) have been implicated in some cases of GW, but plants free of virus and those resistant to virus also develop GW. GW typically develops on green fruit prior to harvest. It appears as black to dark brown necrotic tissue in the walls of the fruit. (Fig. 2). The outer walls are most frequently affected as seen when fruit are cut. (Fig. 3). Blotchy ripening. (Fig. 4). gets its name because the fruit ripens unevenly, with the patches that don't ripen or do so after the rest of the fruit is over-ripe. Symptoms often develop in the interior of dense plants with lots of foliage. Cloudy, wet and cool conditions, high nitrogen, low potassium and compacted soils will increase the severity.