Cracked tomatillo plant
Thank you for the images. Split stems sometimes occur during humid conditions when the plant absorbs a bit of excess moisture. Sometimes, above-ground roots will also poke though the stem in response to the humidity.
The usual remedy is to ignore it . But, if all the leaves above the crack/split fail, the majority of this growth will be lost. Even so, there should be enough time for new branches to develop below the wound. Not much can be done beyond waiting to see what the plant will do next.