I agree, Spectra will get warm,, If I had to guess 100 degrees F. +/- 10. However I don't think this is the issue. I have experienced a similar issue with a different brand of radio. I found the rec. to be going out of tune and then 1 tx would work and the other would not. But both tx would work on a new rec. This doesn't have to be the spectra module but it could be the encoder c/b in the tx alone in addition to the tx. Confirm the tx works on another rec after it is returned. If so,, verify the ? rec. to see if it works. If not replace the rec. and or repair.
I am still waiting for my HT 555 to be returned for a problem of this type also. The TX is not hitec but the 555 responded as you mentioned. My tx is flying other models and multiple brands of rec. satisfactory. Jim