The Oly 9mm uses the standard 5.56 hammer and not the shortened Colt 9mm hammer. If you have modified top of the standard hammer firing pin contact pad, then chances are it is not be lowered far enough by the carrier and being retained by the disconnector. This may be only the case on light load, since a full strength load may have enough force on the carrier moving back to sling shot the hammer past the disconnector sear.
Note: if you are running the AR-15 "L" cut hammer, switch over to the modified M-16 A-2 hammer with the auto sear tab removed. The top edge is higher than the AR-15 top edge and will guarantee that the hammer is lowered past the disconnector hook (just remember to shorten the tail of the hammer to prevent it from contacting the disconnector tail and penning the tail/ causing trigger slap).
On the tail section of the standard hammer, make sure that it is not penning off the back of the disconnector tail. If you have a white telltale sign on the disconnector tail just behind the hook from the hammer tail, then chances are the hammer may be bouncing the disconnector open.
Remember to check the timing of the hammer release from the disconnector. It may need to be retarded, and what you think is auto doubling may just be trigger finger bounce.
Another item that comes to mind is the disconnector spring; make sure it is installed with the large coil side down.
Check the bolt firing pin channel and firing pin's surface. If needed, polish both and make sure that there is not a bur on the firing pin bolt face opening that may be binding the tip of the pin forward. If the firing pin is sticking forward in the bolt during charging, then bingo, you have a bolt acting like an open bolt system and causing the problem. On the same token, make sure that the firing pin’s return spring is in working condition. If needed, get/make a stronger retention spring out of spring coil stock. On a strong bolt cycle slamming home, the firing pin maybe be overcoming the spring’s retention and igniting the primer.
Granted that I may have rambled on a bit, without having the rifle in hand to check, I can just point out some of the key points to check.
P.S. I don’t wander over in this forum much, so if you need me, IM or just post in the trouble-shooting forum if you narrow the problem down.