This appears to be an issue with Webflow as I just tested one of my older projects and including capital letters in the page slugs throws a 404. That said, if I use capitals in my main URL the page redirects just fine (ex: YourDomain.com).
I did a quick Google search and found an older thread here in the community where @samliew was nice enough to provide a snippet of code that should prevent the issue. Just head to your 404 page, then Page Settings > Custom Code > Header Code and include the following:
I haven’t tested this myself but it’s worth giving a shot. If you’re so inclined, I’d send Webflow Support a quick message on the behavior and/or include an idea over in the Wishlist