There's no official Qwen 3.8 4B (only 27B and 2.4T.. at least for now), so if not a typo you've downloaded some third party model/finetune.

Also if you have less than 24GB VRAM, then ollama defaults to 4K context. If that "Qwen 3.8" uses thinking, it might be running out of context and forgetting what it was even answering mid-generation. If that's the case, then try increasing context size: https://docs.ollama.com/context-length , but also: https://sleepingrobots.com/dreams/stop-using-ollama/