The last picture with the plaster missing shows (if I am interpreting the brown stripe correctly) a moisture therefore rust issue?

Is that where the tap fittings were?

Are you running another row of tiles above the skirting (1st row of vertical tiles)? If so, you may find that the plaster set over the hard wall needs to be scored with a screwdriver for better purchase of the adhesive.

Otherwise the tiles are only glued to the paint, which may come away if previous coats were not prepped properly.

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