Ditra under slate tile around a pool

Hi

Have Ditra under slate tile around a very old pool. Some tiles are loose so am having them put back down. Question has come if the Ditra is loose from the slab should we
1) take it up and go without the Ditra
2) take it up and put down new Ditra
3) take it up and thin set the old Ditra back down

Thank you

Ditra under slate tile around a pool