Gemma 4 31B QAT GGUF loads with MTP branch, but outputs repeated - any working recipe?

I’m trying to run: unsloth/gemma-4-31B-it-qat-GGUF gemma-4-31B-it-qat-UD-Q4_K_XL.gguf on an RTX 5090 32GB using llama.cpp Gemma 4 MTP PR branch. Main model loads. Without the MTP assistant head, /v1/chat/completions returns repeated <unused49>. I also tried the public MTP assistant head: boxwrench/g