I made eleven custom structures, all with relatively high spawn probabilities, and out of several thousands of chunks I explored, I found no custom structures. All but one structure have at least than 100 spawn probability set for them (the exception being the Diamond Tower) and I can't find any anywhere. This is not a problem with my observation skills because some of these structures are pretty large, and even the small ones would've been relatively obvious.
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Custom Structures Not Spawning
Status
Works as designed
Issue description
100/1000000 is 0.0001, which is 0,01% which is a very small probability. You should increase this probability rate. Also, biome conditions do not seem to work and height calculation is not working in some cases, but for these issues, there already are separate tickets.