I built a holiday home 8 years ago. The tiles were perfect for 3 years then a few shifted near one of the bedroom doors. These were replaced after checking the concrete slab underneath. 2 years later they lifted again plus 4 others on the side of the bed. These were again replaced after checking the slab. 1 year later we walked in after dinner one night to find that the 2 shifting ones which had been replaced the first time had not only shifted but when my husband sat on the end of the bed there was a loud crack where a line of 12 tiles had risen in a ridge on the near side of the bed. We had all removed and the slab inspected. There were no cracks, just perfect concrete. Why has this happened? I know one builder who walked in to find an entire flooring completely raised with all tiles helter skelter. Weird to say the least. Rising gas from concrete? tropical heat???