I fear our tests are providing false negatives due to being improperly stored and shipped.

We are using the COPAN eSwab UTM SARS-CoV-2 Test Kit (green cap) and self-administering shallow nasal swabs under the supervision of a nurse. We are doing this outside during the day under popup tents in Georgia in August. These kits were being stored in individuals cars between testing days but I did get that practice stopped, thankfully. I mean the kits are shipped in insulated bags for a reason! The tube of UTM says keep between 2 and 25º Celcius (77º Fahrenheit). They are then put in a regular cardboard FedEx box and overnighted to Los Angeles. The lab uses a Hologic Aptima SARS-Cov-2 Assay (Panther System). I know this is not good practice, but I need the specifics of why in order to actually get anyone's attention.

So my question is, what are the potential consequences of exceeding temperature guidelines, and what causes them?

Would the tests simply come back as invalid?

Or could the heat harm/denature/deactivate the UTM and/or the RNA and return a false negative?