I've had some luck in these cases prompting "your context seems to be getting too bloated. summarize this conversation into a prompt that I can feed into a new chat with a fresh context. make sure to include <...>".
Sometimes it works well the first time, and sometimes it spits out a summary where you can see what it is confused about, and you can guide it to create a better summary. Sometimes just having that summary in its context gets it over the hump and you can just say "actually I'm going to continue with you; please reference this summary going forward", and sometimes you actually do have to restart the LLM with the new context. And of course sometimes there's nothing that works at all.
I’ve had really good luck with having gpt generate a todo list that’s very, very detailed. Then having Claude use it to check items off. Still far from perfect but since doing that haven’t run into context issues since I can just start a new chat and feed it the todo (the todo also contains project info).