Every time we flush the upstairs bathroom toilet, it floods the basement shower stall. Which means sewer mess comes out of the shower every time we use the bathrooms. Earlier today we used the electric snake, and it seemed to be fixed. Later that day, it started doing the same thing again.

The clog will be past the down stairss basement shower stall in the main, if the clog was between the upstairs and downstairs, it would be backing up upstairs.

You need to snake the main line.

Do you have a clean out in your basement or crawl? Try opening the clean out. Standing water means the clog is even further downstream toward the city, no standing water you need to snake upstream to the clog.