Steps to reproduce.
1. put those in a texture pack
2. notice the frames on the image below are labeled 0-7
3. launch texture pack and see it repeat 0 1 7 7 ignoring frames 3 and 3
Another form of the issue not displaying last index
1. change the mcmeta file to state 0,1,3 for the frames
2. notice it flash 0 and 1 but, not 3
Another issue caused by or related to this issue
1. copy this text and paste it to the cactus_side.png.mcmeta
2. notice everything is going normal frametime except the last frame which is at least 2 seconds 40 ticks when I set it to 20 if this is intended please ignore it.