Make sure to make your nails flush with the wood.
Floor creaks under toilet.
Clean the flange well or use a new one and install over the drain and new wood.
Place a bucket directly under the soft spot and open a small hole using a keyhole saw.
You may need to scrape the flange with a small putty knife and use a wire brush to get it clean and free of any corrosion or debris.
You may not think of your floor as vulnerable but in the bathroom it is.
Rather than tear into the finished floor i suggest that you start in the basement ceiling where the soft spot is located.
Normally this is avoided if when the wood subfloor underlayment is installed it is glued and screwed so there isn t any movement or chance for there.
Peel back the flooring around the fixture and you will.
The bucket will catch any water that may be trapped in this area.
Remove enough of the drywall to open the area under the shower and toilet.
Repair floor under toilet nail the plywood to the floor joists.
How to fix a rotten floor around the toilet.
Around the toilet the floor may get flooded from overflowing.
I doubt that it is the tile assembly itself moving independent of the floor but that would have to be verified.
With some effort you can slide them back tight again.
A laminate floor in a friend s house seems to be possessed overnight gaps appear in the floor where one piece butts up against another.