I hope this helps and again I hope it is not the case for you but this is what I found when I did a google search for stem splitting.
Most vegetable growers will be familiar with the fungal infection Verticillium wilt, as it affects a wide range of
vegetables as well has hops. The first symptoms usually appear fairly late in the season, as the hops are maturing and often when the cones are half-grown. Leaves will yellow and wither, with the lower leaves turning yellow first. Bines infected with Verticillium wilt will eventually turn entirely brown and will lose their whole crop of hops. Browning and thickening of the lower stem, with splitting of the bine or peeling bark is a constant feature, along with an excessively firm attachment of the bine to the crown, so that when a section of diseased bine is pulled away, a piece of the crown comes with it.
This disease is resident in the soil, so that even if diseased bines are removed and clean bines planted in the
same place, the disease will return to the clean stock. Fuggle is one of the most susceptible varieties, so if the
disease presents itself in a Fuggle yard, it may be necessary to change to another variety.
Water-logging seems to be the most common carrier of this disease. Water must not be allowed to stand on the surface near the base of the plants in wet weather.
Originally Posted by damdaman
Hmm, to me that looks like a split that is caused by lack-of-water-stress followed by large amounts of water being dumped into the soil. What I've seen happen with other plants is that the soil gets too dry and the plant goes into water stress. The gardener figures out at some point they've been neglecting giving the plant water, so they dump tons and tons of water into the soil all at once. The plant then sucks up as much water as it can, causing it to swell up and crack.
Don't know about the browning cones, maybe they're just ready to harvest?