Watch does not immediately restart after hacking

Hi all,

I got a 2-year old Panoreserve.

Recently I noticed that about 1/10 times after I hacked/unhacked the watch, it does not immediately start to move. It would start to run after I turn it or gently give it a shake.
I know it is not a power/winding issue, because I fully wound the watch and the reserve indicator is full.

Is it already due for a service?