► If you "lube" any of this at all, you want to use graphite powder from the lock section of the local hardware store. Mr Jack is right, these primer slides need to be run-in to operate their best. Burr removal is one thing, but don't go removing any material.
► When I got my 550, there was a dragging action on the shell holder. Turned out the primer anvil was 1/2 thou too high. Loosening the set screw and simply pushing it down into the primer slide bar took care of everything. Micro adjustments of the shell plate location and primer slide stop screw were also needed.
► Another biggie is always the placement of the hairpin spring on the loading plate. You want that spring to apply just enough pressure to chase the empty case fully into the shell holder and thereby locate the primer pocket directly over the primer ram. Micro adjustments to the position of the spring have helped me considerably, especially at caliber change time. Watch out, too much pressure and the spring will not allow the rotation of the shell holder.
► And too, consider that it may be an occasional piece of brass with a Mil crimped primer pocket causing this issue. Close inspection of the primer pockets may be in order.
► I've also found that the softer Federal #100 primers typically give more seating issues than say Winchester or CCI. Especially while the press is new. The thicker primer cups seem to bulldoze their way into the primer pocket easier than the softer Federals. I dearly love my Federal primers, but 1 of each 100 will give me a hiccup, whereas Winchesters run flawlessly.
Hope this helps!