Hydrocarbons condensation in isolated line

Hi all members of the petroleum community

I have a question for all of you, may you help me.

In a isolated line that contains a hydrocarbons(vapours) mixture, I can calculate dew point with hysys.This line feeds into a K.O DRUM.

In the basic engineering of the suction compressor drum, It exists a certain amount of liquid.

My question is: How is it possible condensation in an isolated line,if the dew point is not reached.

Thanks in advance

below should be possible alternative explanations:

1. C7+ characterization is not accurate.
2. Drum knocks out liquid during compressor startup (J-T effect across anti-surge valve)
3. If the KO drum after 2-3rd stage compression, during compressor stop, the liquids evaporate slowly from the KO drum due to venting.

Hope it helps :)