Plumbers are not known for their careful consideration of the structural implications of what they remove from a floor. By which I mean, some have a tendency (regardless of the effect on the safety of the mutilated floor joists) to hack away whatever gets in the way of the plumbing they are installing. It does not surprise me how often CSES is asked to provide fixes for the damage done.
This is an especially bad (or good?) example. The plumber removed about 90% of two floor joists, not much in the grand scheme of things, but enough to lead to cracking in the bathroom tile, even if the residents do not fall through the floor. Still, it is kind of interesting to come up with repairs that don’t break the bank. Oh, the glamour of this job….