Anyone else have this problem?
Daylight hours, using a homebrew bowtie array I get multiple stations.
As soon as the sun disappears, all I am left with is a very local ABC affiliate and 4 channels of WTCT religious programming.
Could it be the tv? I am using the onboard tuner in a TruFlat RCA, not a converter box.

Was this happening in the winter, too?

Sometimes, especially when the weather warms up, conditions on the atmosphere near ground level can cause distant stations to travel beyond the horizon (a phenomenon called tropospheric refraction). This sometimes allows people to see TV stations (even UHF) at great distances, but, it also causes stations to interfere with each other (for example, if analog channel 32 in Louisville were to become very strong at your home, it could wipe out your digital reception of WPSD [NBC])

One would think that with 906 kW at 492.0m, from only 44 miles, that WPSD-DT should be durable.

Is your homemade bowtie on the roof, in the attic, or on the set?

Could it be the tv? I am using the onboard tuner in a TruFlat RCA, not a converter box.
If it's an older CRT set with a built-in digital tuner, it could be the tuner. They have made great strides in the newer generations of tuners. First one I tried a few years ago wouldn't receive but a couple of channels here. Newer tuners and their digital signal processing have improved reception greatly. So you might want to try a newer DTV converter box just to see.

Have the antenna indoors now, hanging from a plant hook in the ceiling.
I can receive WPSD-DT out of Paducah, and can get most days a CBS affiliate out of Evansville. But at night they disappear. What is really puzzling is the number of stations, and the quality of the signal I can receive in daylight hours.
I kinda suspect it is a combination of poor antenna location, loss through the coax cable, and the onboard tuner.
Just for giggles I took a set of rabit ears, collapsed the dipoles, spread them in the horizontal plane, and placed it on top of the set. It works, but again only in daylight hours.
Guess I need to experiment a little more.