They are slippery in my experience. Make sure the cap that holds the compression sleeve in place is screwed down tight. Could be the compression sleeve is worn out, it happens eventually. You could try to roughen up the stem with some fine grit sandpaper, say 220 but they are expensive to replace. If your pump has Schrader valve option try screwing on a Presta to Schrader valve adaptor. I’ve done the last option and it worked.