What cases are you using on your iPhone 7 Plus?
Realistically, it will be because there is less structural integrity on the left side due to the ringer/mute switch hole being there, that will always make that left side a bit loose, and mine is a bit loose from looking at it sternly, but nothing that compromises the case. you can see this as you push the rubber outwards near the ringer/mute switch and slowly work your way down toward the polycarbonate exterior. It's not a design flaw but rather just quirk. It shouldn't affect the protection that this case offers, and if you're ever unhappy you can get a fresh new rubber inner piece from OtterBox warranty claims, although I think they charge you shipping & processing which is like $4-5.
Originally Posted by johnc847
Over time and heavy usage, it is only normal that the rubber on the sides will get a bit loose over time, that is with anything. I was a bit OCD with it on my iPhone 6s but that was because that Commuter version had a very poor fitment issue that seems to be alleviated with the new Commuter. I'll post up pics to show you exactly what I mean.
EDIT: pic uploaded. Notice the rubber lacks a solid form. Buttons leaning downward, not straight, and the rubber by the ringer/mute switch is thin, and loose, exposing lack of true fittest. This is something that has been greatly improved over the previous Commuter.