Tailgate opening delay

When I pull rear gate handle to open it I get initial click but it does not release fully, few seconds later there is second click and I can open the gate. Sometimes it opens at first try but usually after driving around. Any ideas why it does that? Battery is fully charged but old (reading 11.9 volts when cold) I've new tailgate latch due to corrosion in old one but old one behaved the same with delay click. Is it multiplex controller module or something else? I didn't see any corrosion on cables or in door hardware while in there.