for vBulletin, unfortunately, every guest visitor will be set cookies, so it'll not working as you expected. caching vBulletion for guest users is a bit more complicated, but it's possible under litespeed. In fact, we've tried to cache this vBulletin (litespeed suport forum) for guest visitors for a few weeks and looks working well. We can open an new thread to discuss our implementation to cache vBulletin under litespeed.
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