Sounds to me like the contractor may not have done the job right.
If this does not help the only solution may be to redo the entire floor, tile and all. Use a product called “Hardibacker” screwed into the floor joists using the special screws made for this application. This is a ¼” thick cement and fiber based product made for use under ceramic tile. Be sure to stagger the seams. (Check the floor very carefully first to make certain there are no weak spots that are deflecting (even the slightest bit) when walked on. If you find any they must be repaired first either by cutting them out and replacing them or by adding additional blocking underneath. The sub floor MUST BE devoid of any soft areas prone to deflection.
Good luck and I hope you do not have to re-do the entire floor.
Also, the cracks run along the grout were it meets the tile-dont know if that makes a difference in your opinion. Also have discovered that the plywood was stapled to the subfloor (dont know if nails were used at the joists). Let me know if any of this affects your opinion. Thanks again for all your help.
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