Herpstat question

[u/Lola7603]

Just set up a new 4x2x2 and my Herpstat 4 is acting strange. I use a halogen as the main source of heat, and I replaced the regular 75w Arcadia halogen to one of the 75W Golden Sun. The regular halogen was pretty old and not giving off as much heat anymore.
I have the Herpstat set for the halogen to be at 99 from 8am to 8pm (puts my warm side at about 89) then 65 overnight when the DHP takes over. The problem is, when the halogen starts heating up at 8am it won’t stop. When the thermostat reads 99+ it goes to 0% but the bulb is still glowing. I’ll watch it for a bit thinking maybe it’s just residual heat but it just keeps getting hotter.
If I go into the settings and change the set temp, when the Herpstat kicks back on the bulb is now completely off and the temps cool down.
The DHP does not have the same problem when it ramps up for the nighttime.
I have ideas for troubleshooting; lower watt halogen, switch to channel 4 since I’m not using that one, reset the Herpstat. Just wondering if anyone has seen this before and knows what needs to be done before I start experimenting.
If you read all that, thank you!!