Do you have the service packs installed? 2017 release had a bug with Transform Cache durring animation playback. It really only affected IK the way you demonstrate. Try updating and if that doesnt fix it google how to disable the transform cache in 2017.
Hello everybody. I was a modeler all along, but I wanted to practice animation now as well, so I created a very simple rig for a cylinder. I'm animating the cylinder with a shape that's linked to a point helper, which is linked to the IK end effector. As you can see in the gif below, the frames from 0-26 work perfectly…