[ramarar]

I was doing taxi missions when i took a passenger from portland docks to noodle punk. After that when i ignored the first person who wanted to enter the cab and then again the same one comes and asks me to drive back to portland docks

[Shayan Shaffey]

The way I'm understanding this, it's not a glitch, it's just those NPC's that are assigned to enter your cab, nothing abnormal here.

[Nukey Shay]

Correct. If you have trouble finding quick fares (such as in Trenton), you can knock riders off bikes...who stand pretty good odds of flagging you down for a lift

You may also get a destination request that is the same as the one you just left after dropping off.

[Shane X. Walsh]

Its not even a glitch. This is just another NPC or peds wanted to visit/go into the same place.