Check the set screw for the shell seating post,it may have come loose causing the shell seating cup,to float high?Depth adjusting screw not adjusted right?Possibly over sized fiochi style primers got mixed in with the US style primers?Something blocking the retaining pin that holds the shell down in sta 2 for resizing?Check for spilled shot underneath the main shaft?You can stop the reloading
process and remove all the dies but one and try and seat a primer,this should lead to narrowing down,your problem?Also possible,sticking primer shaft,or loose prime cup bolt,start from basic's and work forward,you will find it?
U Tube has a Spolar trouble shooting video that shows how to adjust the primer seating depth. If you have an older spolar you will not have a set screw for adjustments for the cup. You can also call Carter or Dixie at Spolar, they will be more than happy to help.
You might have had the weight,that sit's on the primer seating shaft's set screw come loose and or after cleaning the primer shaft if you have taken it out of the machine,if you spin the weight on the shaft and don't have it set right,it will ride lower than it should be making your primer shaft,not go to the proper height and give you that condition?You can also have the weight,set so that it can possibly hit the bottom of the aluminum piece and this will impede the primer shat from getting to it's proper height.I have done that in my loading career,at times,but no more.
You are lucky that you didn't break anything else when that happened,there is a part called a wad cam dowell pin that actually makes that arm index.It can break under if enough force is applied to the
assembly,I know, I broke one many years ago.If this happens the wad assembly will swing widely out of it's normal position and when the wad ram comes down under force to seat the wad,you can get a bent assembly.The wad seating ram can come down and strike the aluminum wad guide fingers part.Most people will never know that they have this part,or what it does?
Yepp,that happens,shot will find it's way to any place it can,one spot to look is when you spill shot,a piece will get into the little V-notch on the wad cam block and it will rest there,when the pin comes down,it hit's the piece of shot raising the wad guide assembly just enough to change your wad seating depth.You really don't realize it's there even though it's right in front of you,with good before
reloading,check practices,you will notice this potential,problem.Before I start a run of shells,I do a pre check,of trouble spots and then proceed,to load.