I have this behavior the first call returns values using JanusGraph query
JG.query().has("geo_shape", Geo.WITHIN,
Geoshape.circle(12, 13, 100.0)).vertices().count()
while the next line doesn't return results !
val c = JG.traversal().V().has("geo_shape",
within(Geoshape.circle(12, 13, 100.0))).count().next()
According to the query examples your query should look more like this:
JG.traversal().V().has("geo_shape",
geoWithin(Geoshape.circle(12, 13, 100.0))).count().next()