Odd situation with soft floor around toilet

[Ronald1276354]

the area around our toilet is soft and I can hear squishy sounds when it’s presses. The odd situation is the toilet will run for 5 minutes or so after a flush but if the shower is running and the toilet is flushed, the toilet will run the entire time the shower is on.

The area around the toilet being soft I have an idea of and will know for certain when I remove everything tomorrow

What I can’t understand is the shower running and causing the toilet to run the entire time.

 

[Stuff]

Shower running causes lower water pressure so not enough for fill valve to close. Easiest to replace it.