Single-family Florida concrete block home built in 1979, city water and sewage.
Hallway bathroom toilet flushes great, quickly swirls, drains completely and quickly, refills.
Master bedroom toilet, however, nearly fills to overflowing and then very slowly and unenthusiastically drains. Unlike the hallway bathroom there's no satisfying swirl followed by that climactic gurgle as the toilet sort of catches its breath. Flushed it and heard no sounds from the shower drain; shower and sink both in the master bedroom drain quickly. While sitting in the hallway bathroom after flushing the bedroom, no bubbles nor gurgling from the hallway bath tub nor sink drains.
Tried plunger, sink auger, toilet auger, no significant effect. Tried Liquid Lightning™ (sulfuric acid), negligible difference after a full bottle. Went up on the roof to look down the vent, no sign of nesting squirrels or debris at least within sight of my fairly bright LED flashlight.
Have a few trees, including a big pine tree near where the drain line goes to the street in front of the house, as well as a hickory tree and a couple of sweetgums farther away from the drain to the sewer. Could this be root intrusion even though only one toilet is affected?