I discussed this issue with Ramba from technical support (Support TicketID : 207203) and tried the following: 1-Optimized the keys using the Curve Editor plugin. 2-Excluding the torso from resampling. But, none worked and the sliding Issue is still persist, so Rampa referred me to report this bug in Feedback Tracker.
The only ways to stop this issue from occurring are: 1-Breaking the clips to smaller clips to prevent the sliding issues and to prevent slow performance when using sample motion clip option. 2-By using edit reach target option, reach effector to stop the foot from sliding.
Is there a fix for this issue to make me able to use sample optimized properly?