Recently, watching Youtube streams has been terrible on Opera One.
With chat closed it works fine, but if chat is open Task Manager shows that RAM usage for that tab increases by ~50 MB per second without stopping until the tab crashes (out of memory). After only a few seconds, the stream starts struggling hard. CPU usage also increases 5-10x, but that's normal. Closing the chat (i.e. not the tab) stabilizes the tab, but it does not dump memory usage for a while.
Without chat enabled, the memory usage stays low and stable, correctly flushing video data rapidly from the RAM. So this only applies to chat, and it's probably worse on very active chats (streams with 5k+ live viewers) than slow chats.
Currently on Opera One 109.0.5097.59, but this has been going on for a few recent releases (maybe after 108.x or 109.x). This was not an issue a month or two back, running on the same system as today.