Help! Tiles falling off in shower

[Bridgette01]

Hello All, Half the tiles in my shower are falling off or about to. The tiles were originally fixed in place with what appears to be 1 or 2mm of tile adhesive (see photo) The back of the removed tiles show a very small contact area with the adhesive. There is cement sheet used as a back board and it appears to be pretty much dry. I suspect this cement sheet has asbestos contained in it as the house is built in the 60's.

I am able to simply peel the old tile adhesive off the cement sheet (or simply flick it off ) and re glue and grout the tiles back on. Any thoughts would be appreciated.