If the vinyl is at all cushioned you cannot set tile because of the compression due to the cushioning. Poke your fingernail in it, if it compresses rip it out.

If it is a full sheet is it glued down 100% or just along the seams and around the perimeter of the room? Is the glue holding it down really well or is it dog eared in spots? Anything less than full strong contact will not work under tile.

You did say this was over cement. Are there any cracks in the vinyl due to movement cracks in the cement slab? If so, the vinyl may be hiding other cracks that have not transmitted up yet but will and cause the tile to crack.

Is it a no wax floor? Vinyl does not offer a greta bond for tile thinset to begin with, any wax will cause the thinset to not bond at all.

If this were a wood subfloor, tile should never be set over the vinyl and whatever is under it. All that junk needs to be ripped out. Going over cement you are rolling the dice. I would not advise it but it has been done successfully, but then again so has running a stop sign.

other than what Bob has stated, please consider the following.

you new isntallation will only be as good as your existing flooring system.

experience has taught us to never installtion over any resilient product.

We always remove existing resilient products (vinyls, rubbers, linoleums).

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