The only thing I can think is that you aren't giving SR time to spool up. When you have SR on, you press down your shutter halfway and the SR will activate. However it takes time to activate and there is a green hand symbol in the viewfinder that will light up when it is active. Before that symbol is lit up, you are shooting without SR. See pages 139-144.
https://www.ricoh-imaging.co.jp/english/support/man-pdf/k-5.pdf
I suppose the other possibility is that you are simply experiencing shutter shake, which typically happens in shutter speed between 1/20 and 1/100 second.
The SR is automatically switched off when using self timer and remote activated modes too, but I can't imagine that is what you are dealing with.