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It means the conflict is with Yoast. Try to deactivate it and test.
Tested by deactivating both yoast and AIO. No titles were generated.
Ok, then this is not SEO plugin conflict. I see wpForo SEO works fine for meta description. Only meta Title are not being replaced. This comes from theme, it seems some hook is not properly used by theme developers. There is a WordPress Theme Codex issue with this theme.
Also please deactivate other plugins too and delete cache + do Ctrl+F5 on forum pages before checking.