Pictures Failing mosaic tiles on shower floor

I bought Faulty Towers last June. I have done a fix on my shower floor tiles. It has lasted for a couple of months but is now failing again.

The problem is mosaic tiles coming off. I tried siliconing them to the adhesive base then a bit of grout in the gaps. So, that doesn’t work.

Is there a permanent fix? Could I carefully sand down the adhesive to a flat surface then apply new over the old?

All suggestions welcome. Many thanks in advance

If it’s just a couple of tiles that have popped, it’s unlikely to be any other issues other just failed adhesive on such small tiles.
Silicon won’t hold the tile for long and because it is so flexible, will allow the tile to move and cause your grout to crack.
Your best bet would be to try and carefully chisel/scrape up as much of the old adhesive as you can then mix up some fresh tile adhesive and stick the tile back down with that.
Give it some time for the adhesive to cure, refer to the product packaging to be certain, but usually after 24 hours you should be ok to grout. Once the grout has cured you’re all done 👌🏽!
Hope that helps.

An alternative is to bust up all the tiles in the shower floor and redo them all but worth a try at patching first.