Happens every now and again. Radio interference from routers, microwave ovens (usually from the control circuitry, not the magnetron so don't panic) or anything that generates a radio signal can potentially interfere.
It could be a one off due to any number of factors.
If it happens often where you park, Lexus can change frequency which may solve your problem, it just depends what and how the signal is being blocked/distorted.
I know a couple of spots that I cannot go to as the key simply will not work, even with it touching the start button.