Hi Km,
[quote] A few weeks (1-2 months) ago I noticed that the top two layers on my spouses side had shifted due to the appearance of a bulge along the outer edge of her side of the mattress. I unzipped the mattress and confirmed that the top two layers on her side had shifted away from the center by approx 1" (top layer) and .5" (middle layer) . I inquired with EZ about potentially gluing the halves together and I believe I also asked if there was something which may cause the shifting. I had not received a reply. I also conversed with our resident expert (Phoenix) via pm as well.
It was suggested that perhaps the sections were stretched when the bed was built and that resetting the sections in a more relaxed/normal state would prohibit the shifting. I rebuilt the bed trying to make sure the the cover as square as possible and added the sections with minimial waving.[/quote]
The issues you are having are certainly not the norm with split layering so I’m certainly curious about what may be the cause.
The only things that could normally cause these types of issues that I could think of would be either putting the mattress together with one of more layers somewhat “bunched up” inside the cover where part of the layers are more stretched and part are more compressed (this would be the most common reason), an issue with the foundation underneath the mattress, moving the mattress, or the cover loosening or stretching more than normal (unlikely but possible).
You may need to do a little more than “minimal” waving to put the layers into their ideal position where they are square and not stretched outside of their “relaxed” shape because latex can be very stretchy and it’s very easy to put the layers inside the cover with the inside part of the layer stretched a bit and the outside areas bunched. In these cases you would need to lift the edge and “wave” the layer into position at the same time as you are “pushing” towards the center so that the layers are more evenly compressed and distributed (you can see an example here of another member that mentioned how the layers didn’t seem to be the correct size or fit right inside the cover). If anything I would try to make the middle a little more “bunched” and the outer edges a little more “stretched”.
I would also check the foundation just to make sure there are no issues underneath your mattress that could be allowing some areas of your mattress to sink into the foundation more than the others which could cause layers to shift.
One of these should solve any shifting issues you may have but the first step would always be to phone Shawn at SleepEZ because he may have some additional suggestions as well.
If you do decide to glue the layers together then you can use a glue such as here or here and any upholstery shop should also be able to provide you with a spray glue that would be suitable. While it isn’t really necessary … I would try to match each side as “best practice”.
ADMIN NOTE:Removed 404 page link | Archived Footprint: sleeplikeabear.com/Latex%20Foam%20Project%20Tools%20Latex%20Glue%20and%20Accessories
One other suggestion is that it can be a good idea to flip the layers (or at least the top layers) once or twice a year because it can help even out any compression over time and slightly extend the life of the layers (see post #2 here). While this isn’t “necessary” because latex is already the most durable foam material anyway … every little bit can help 
Phoenix