How many slices are you using?
Rytm uses 120 slices, so 60, 30, 15, 12, 10, are best.
Octatrack uses 128, so 64, 32, 16, 8 are best.
I like the 30 length for Rytm myself, I find it easiest to manage on the Rytm, and it gives you plenty of hits in one file.
Here’s my screen shot of a 30 slice waveform prior to rendering in Ableton Live. These were MachineDrum Kicks. Notice the highlighted selection goes all the way to 31 (the end of 30).
Also, make sure to turn off “Create Fades on Clip Edges” in Live’s Record/Warp/Launch preferences, if using Ableton Live. (especially if you’re doing single cycle waveforms). Also make sure to not go over -3dB on the file, as Rytm will distort samples by default higher than -3dB. As discovered by the kind “gbravetti” here: [Solved] The RYTM sample engine can't play dry samples