Shower Drain Installation What Might A Sour/Musty Odor Coming From Shower Drain Be?

What might a Sour/Musty odor coming from Shower Drain be? - shower drain installation

House has been employed for 7 months and had recently replaced a shower. Used in the same location of leaks, including catch and escape through the roof.
There were two toilets STUDOR new plumbing and ventilation systems installed. Originally it was believed that ventilation STUDOR new smell may be defective, but the smell of the shower, sink.
Shower now have used a dozen times since the installation, but the smell back.

Shower and vanity are used again for 2 weeks after installation, but still the smell.

Looking for suggestions on a possible solution. Thank you!