Hello,
Thanks for the detailed explanation

Since the THA-250F works with other DMX controllers and other fixtures work correctly from the CueCore2, this does not currently look like a general CueCore2 DMX output failure. My first suspicion is that the fixture is sensitive to the normal DMX timing.
Please try enabling
Slow DMX in the CueCore2 under Settings → DMX. This option is specifically intended for fixtures that have difficulties with the normal DMX transmission rate.
For the test, if possible, connect only the THA-250F directly to the CueCore2 with a short known-good DMX cable and a 120 Ω terminator. Also check whether the DMX Signal LED on the rear of the THA-250F starts flashing.
If it still does not detect DMX, please let me know the CueCore2 firmware version, whether the same happens on both DMX A and DMX B, and whether you are using the 3-pin or 5-pin connection with any adapters in between.
Hope this helps!