Hey, thanks for the report. This is a known bug in 2.6.11 and 2.6.12 related to a specific chat panel layout state.
Workaround: Click the double-arrow icon in the top-right corner of the chat panel to switch away from the Classic layout. After that, chat history should work normally.
More details and discussion here: [2.6.11] Clicking On Chat in Chat History Not Working
Let me know if anything else comes up.