Actually, yes. I think what happened was a combination of a stupid move on my part and my under-estimation of hatching time. (With our cold weather - the tank went to 69-70F - not the 71F that I ideally like)
I have 4 crystal RAnchu. 2 male, 2 female. The first day, the red female dropped eggs. The second day, the red female and the red/black female dropped eggs. The third day, the black/red female dropped eggs. And then I left the mats in for one more day (and I think there were more eggs, then) before pulling them and putting them in the fry tank.
The eggs hatched on Sunday, Monday and Tuesday. Wednesday, late afternoon, I pulled the mat, shaking off any clinging fry - because I wanted to remove unhatched eggs before they went to fungus. I think what I was seeing were just eggs that had not hatched, yet. I jumped the gun.
I think thatwhat I was seeing was a large number of freshly hatched fry - before they were free swimming. I was comparing them to the others that were hatched a day or two earlier - already free swimming and eating voraciously. By dumping them off their perches on the spawning grass, I limitied their oxygen uptake, as well placed them lower in the tank with less resting places to use on that all important dash to the surface to fill their little swim bladders.
I put a plant back in - one that reached to the surface (still only 6 inches deep) and watched. About 1/2 of the belly sliders did, eventually, make it to the surface and become swimmers. The other half, unfortunately, I am going to have to chalk up to my learning curve - I goofed I think. My fault.

I will not pull the plants and mats too soon in the future. I hope.
I have hundreds of fry, though. More than enough. I hope I will be able to find some nice Japanese bodies in the group - and if I am lucky - a Crystal or two!)