Forgive me for not replying to this sooner!! I’ve had a lot of real-life stuff going on and it’s been difficult for me to cope with everything. ;o; I know your problem is probably already fixed, but I’ll poke ya about this anywei. 

So- First off, you’ll need to go to ‘File’ and then to ‘PMX Info’. Scroll down and you’ll more than likely find those 20 centre bones down there somewhere. Look at the number they provide for when going through ‘display pane’. Usually- I’m so lazy that I just go ahead and delete all of the folders in there and then create new ones titled; “Bones”, “Extra body bones” and “Misc. Bones”. Then, I usually spam the ‘Bone: ___ +Add’ button until I get them all in their proper slots- but if you want to do it the proper way, just select the proper bones from the ‘Bone’ tab and ‘Copy Index’- then paste in the appropriate folders. Then, you should be done! If you have any questions- or if I worded anything wrong, just ask and I’ll clarify QuQ <3