Just failed to transfer the image from the die to the coin blank. As the die filled with grease the image became less pronounced. Very common, especially on pennies due to soft metal and only worth face value. The Mint has more than one machine that produces coins. They have numerous machines, all producing the same penny. Slight variations occur as each machine has it's own die. Due to the high number of coins produced by these high speed processing machines, grease fills in the low places on the die and it's transferred to the blank coin (planchet). The result is what you are seeing here. The high points on the coin appear low. Not an error. It's what I refer to as cheap coinage.