Dump the powder out of it and take the metering insert out of it and cycle it without the insert. You may have to hold the drum in place but it will still indicate if the metering insert has any bearing on it.
If it still has the problem than you know it's the linkage.
If it is still doing it, put the insert back in and take the stop bar off the side of the measure, put spring back on and see if it sticks then.
If it is I would check the to screws at the top of the linkage
View attachment 1110282 these are lock screws and nuts, and one may be binding at the top if they are to tight.
If you follow this you should know by know what area is causing the problem.
If non of this works than ask Hornady for a shipping label to send it in and have it fixed or replaced.