Having explored some of these nests in person, here's some observations

Dataran Petaling Jaya: Jynx spawn is not often. I noted that only 2 spawn points in this location will spawn Jynx, and these are usually timed at the 0 to 5 minute mark past the hour. One can be reached while walking from A&W, the other is in the middle of the field. When I came here pass the 30 minute mark, no Jynxs Thankfully A&W provided waiting relief

Taman Jaya: This seems to be more of a general water biome than a Jynx nest. When I came here at 2 differing times, no Jynxs were in the sightings. Good thing this is close by Dataran Petaling Jaya so I could alternate between the two.

Kompleks Sukan Astaka: Shellders only appear in the field =.= the field is muddy after the rain so its a real pain to get to the spawn points. Stinks like cow dung as well. Agony