The small eagle should be a Eagle over an N which became the standard German proof mark in 1940, Previous mark was a Crown over a N. Your gun was made in 1940/1941. With no other markings, it is a commercial gun sold to the public, it was not military issue. The Walther PP is a fine well made gun but it has its quirks. It is not unusual for an automatic pistol to dislike a certain brand of ammo, I think it's voodoo or black magic. The prices for everything WWII has gone up so much in the last couple of years I will not even try and guess-a-mate the value. Someone else can have that pleasure
Pictures would be a great help in making sure the information I've given is correct.