So I went to spend 18 diamonds earlier and I clicked forge and nothing happened. I seen everything glow like normally but no numbers came up. It took my diamonds, and now APPLY button appeared. It just happened to me the 3rd time again today! Like, what is going on. It's stealing all of my diamonds!
The value for each stat is random, it can be 0. If it is 0 for all 3 stats then it will show like that.
Also, if your base stats are high enough it is very unlikely that you will get positive values without using higher forge values. With 18 diamonds you will only get guaranteed positive results up to +40 stats. it will give positive/negative up to +60 and mostly negative after 60. You can read more about the forge here: http://soulhuntersheroguide.com/forge-guide/