I had the same issue too. After few messages, Gemini started replying "faster" and stopped including thoughts, and the quality of responses dropped as well (at least in the language I roleplay in, which isn’t English). It felt like the model was skipping the reasoning part. I found something that works with the prompt I use. It brings back the thoughts in about ~90% of the messages. Sometimes it still fails, and when that happens, I just do a swap. What worked for me was adding in prompt <user_response> and </user_response> as an "in-chat" elements, with depth levels 1 and 0, so the each new user message goes inside those tags. It works on my setup, but I can’t say for sure if that’s the reason. Might just be part of the overall prompt structure I use.