1) the first likely culprit is flashing around the wall and flooring of the porch area.
2) another area could be the caulking and of what caulking material. Here I would use only butyl rubber caulking.
3) Another could be the roof paper or tar paper or building paper being torn, not included, or not overlapped properly.
4) Another could be that the floor needs to be tared underneath before all the flooring installed.
5) Grouting could be leaking also. Grout is porus and may need sealing.
6) Does your porch have a built in "fall" or slope to carry water off and away?
* my list could go on and on, it could be one or all of the above. Would just need to see it and talk to you about what you did underneath the tile to shed water as a secondary precaution.
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