Remounting an undermount sink in a manufactured stone benchtop
An undermount sink needs to be mechanically supported from below, with brackets or some kind of structure that can physically support the weight of sink. Between the water, dishes, maybe even someone leaning on the sink, and the sink itself, we are talking about a load on the order of 100 pounds or more. So definitely far in excess of what an adhesive can support in this layout. In the absence of proper support, the weight of the sink may be resting on your drain pipes, which they are not designed to support. You need to get and install a mechanical support, either brackets (the sink's manufacturer probably makes or recommends some) or a custom-built wood structure to carry its weight. While you're at it, make sure to reseal the edges using a consistent layer of putty or silicone caulk.