Have you ever gotten your finger caught in a Chinese finger trap?
The design flaw in the standard Lee plug is the 1/8” long straight section before the plug’s tapered expansion. When the case is flared, and the loading press ram starts to go back down, the straight section of the plug and case act like a Chinese finger trap. This is the cause of your “tug”, or the cause of excessive extraction force when using a Lee expander.
You can fix your Lee die for free.
The expander plug is titanium carbide based on grey color and spark color when grinding. Using a grinder or a grinding wheel, remove the 1/8” straight section. Put outside radius on your grind. Use lapping compound or steel wool to polish the expander.
The expander plug on the left is a Lee 380 ACP plug, unmodified. At the bottom of the plug you can see the 1/8” straight section and transition to flaring taper which does the work to flare the case mouth. The tip is also dull grey color and not polished.
The expander plug on the right is a Lee 38/357 expander plug, modified as described above. You can see how much I ground the 38/357 expander plug tip by comparing it to the 380 expander plug. Your new radius should transition into the flaring taper section, as shown. The tip is shiny because it was polished.
Simply polishing the tip, and not grinding, is good for about 10 to 20 cases, and then sticking will occur again, in my experience.