That's not going to be fixed with a different LLM model though. I'm experiencing similar problems. If my stt is bad then, then the LLM just gets even more confused or requires a big model that doesnt run efficiently on my local GPU. won't trigger my custom automations because the tools don't consider custom automations phrases.
Speech2phrase improves accuracy for utterances that are basic like turn on X, or anything specified in an automation, but then struggles for other speech.
My next project is to implement a router that forwards the utterance to both speech2phrase and whisper and try to estimate which is correct.
Sorry, I don't fully understand your setup or the problem.
Seems like it's modbus <--> node-red <--> MQTT <--> HASS?
But you want to cut out node red? So if the input to MQTT is slow, what's writing that MQTT value?
Without having any more context, I think I'd reach for Wireshark/tcpdump and just see the packets come in and understand timing.