Hi ejcrossl,
All foam materials will both soften (virtual impressions) and/or develop visible impressions to some degree over time and won’t stay perfectly flat but if they are higher quality and more durable materials such as latex they will be significantly less and take longer to develop than lower quality and less durable materials and any minimal softening or impressions won’t generally affect the comfort and support of the mattress. If there are natural fibers in the mattress quilting they will also develop slight impressions over time as well as they pack down under your weight over time.
Latex in general is the most durable of all the foam materials and generally holds up very well for a very long period of time but there are several possibilities that can account for your experience that are listed in post #4 here.
Softer materials are also less durable than firmer materials of the same type and it’s possible that your mattress was “on the edge” of being too soft for you and even a very slight amount of softening was enough to take you outside of the comfort/support range that is suitable for you.
It’s also possible that there is some sagging in the support system under your mattress which can certainly cause visible impressions.
You can check for any visible impressions in your latex layers by putting them (or the individual layers) on the floor and then either running a string from edge to edge or use a straight edge (such as a broom handle) across the layers and then measuring the depth of any visible impression from the bottom of the straight edge or from the string.
While it would be unusual … if either of your latex layers are defective and there are visible impressions that are deeper than they should be then I would certainly talk to them about a warranty claim.
Phoenix