This was a bug back in September 2020…
I have not had any issues with the instant fuse lab since my original lost Gorgosuchus which support fixed.
I used it today to fuse 2 lvl 30 Gigantophis and it froze on the screen where you hit the DNA cost to fuse them. And froze in that I could hit the DNA button all I want and nothing was happening, however in the background the coins on paddocks were still bouncing up and down and a code 19 in the background was still running. I had to exit the screen (not the game) I went over and checked the instant fuse counter and it was still at three (so it didn’t use a charge) but when I went to the Biodome to go try again… Sadly… my 2 lvl 30s are no where to be found .
I don’t know if the fact that I went from the standard creation lab after the fuse to level 21, fed and then went to combine the two lvl 30s is what caused the issue or if this was a freak occurrence, anyways buyer beware in case there is a new issue that has cropped up with the latest update.