Ls460kev

So I purchased a 2008 ls460 this year in January and it came with these 20” inch aftermarket rims that the previous owner installed. When I drove it the first time the tpms sensors weren’t installed on the wheels which I deemed unsafe because of the low profile tires it had on and it was my first experience with such a wheel size. I went to my local sams club to get the TPMS sensors installed to keep an eye on the tire pressure. I bought all 5 sensors including the spare. The sensors worked at first but after about 20-30 minutes of driving the car the tire pressure warning light came on, I took it back numerous times to have it checked and reset but still had the same results. So I came to the conclusion that the big wheels were causing the sensors to malfunction and decided to buy some new 18” inch wheels that fit the OEM standards and new tires all around (sorry for the long explanation I just didn’t want to leave any detail out) after all this my tire sensors work but the spare tire keeps saying “checking” and thus triggering the warning lights but if I continue driving the car for another 20-30 minutes it turns off because it reads it again. Anybody else have this problem? The sensors work because they get read by the system but maybe my spare is positioned wrong?