Sounds like some liquid has either been spilled on the surface and filtered down through the joints or the adhgesive used was rubbish in the first place. The other thing it could be is a damp floor because of a faulty damp proof membrane.
In all three cases the adhesive has obviously been affected and there is no quick fix here. If the adhesive is tacky and soft then something is wrong and it would be a big mistake to deal with thye effects of this by coivering it up as you need to get to the cause.
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