Change model from multi-modal LLM to text LLM 400 error

[liHai001]

step 1: chose a multi-modal LLM(Ovis2.5-9B) chating, (upload image and chat)
step 2: change to text LLM(Qwen3-30B-A3B) to continue chat on the same conversion.
got error:

there is no logs in the error_xxx.log file

back-end output: