lifter preload

Hello to all.
I am in the process of finishing my 545 and have question. I have hydraulic roller lifters and in adjusting them all seems to feel good except for two, and when I take out the free play and then give it a half turn for preload there doesn't seem to be any resistance on the wrench. All others I can feel a slight resistance. Is it me or do I have a problem? Thanks in advance.