Not enough evidence
If you happen to be experiencing sensitivity at the gumline after using your trays/strips, it is possible that the gel is causing that.
However, it is not likely that gel is causing any recession. You may also be noticing it more, since the dentin
where the enamel
stops will not whiten as enamel does and you will see the difference at the gumline more so with the enamel becoming lighter.