a  few things  causing   skipping,  or  riding-over-  (machine wise)

even though you replace teeth as they break,   the  one's  still there are shorter,  so the  circumference  isn't  as  round as it was.   When the new tooth hits,  it's  lifting  the wheel,  and  the shorter and  worn tooth  right behind it  doesn't have near the  'bite'  at least temporarily.     

We all know   soon as the teeth are on top of the windrow,  it takes  time for it to work it's way  back down.  

worn bushings,   twisted arms or  wings-

The angle of the wheel  (vertically)   has to be tilted so the tooth is  out front,   flipping the  material ahead.      If the wheel is  tilted  so the  teeth are  constantly dragging  from behind,   it's never going to recover when it  rides over the material.     When you are  standing in the middle of the 'v'  the bottom of the wheels  has to be  closer to you than the top of the wheel...  like  6 inches closer.   
think of it opposite  to a  spring tooth harrow, or spike drag..   What angle causes material to bunch and plug.... and what angle allows material to pass?   

A  hay rake tooth has to be  vertical or slightly leading to carry, and 'flip'   the now-rolling  windrow.   if  its  angled back,  the 'flipping' action now is a 'jambing'  the windrow  down against the ground

a  common mistake as a rake  ages,  and begins to  leave  material, is to increase  down pressure.   This only  increases the  wear the wheels and teeth receive.  
rakes are built to  move hay,  not  dirt.

follow behind the rake  at-speed,  and  look how the wheels are flexing  backwards  when  loaded, and up to speed.   

Worn teeth and  holes at the bands,  teeth that have lost their springy-ness,  all contribute here too.