Water coming up from basement shower drain
I have a home built in 1920 with likely all original pipes and drains. Over the last year I've had 3 or 4 episodes where the basement bathroom shower would not drain and then when the upstairs bathroom was used, water would come out of the basement bathroom shower drain. I've had two plumber out to evaluate. The drain has been snaked multiple times. The floor drain has been opened and snaked. No obstructions found.
I currently have water in the basement and I can't afford to pay for another plumber who can't resolve the problem. Can you help?