Thanks! @matthew08m.dev for pointing it out that I need to pick the main URL.
I have chosen www.mysite.com to be the main one and to have mysite.com redirect to www.mysite.com

I have waited a day for everything to propagate so after 24 hours, things seem to work. But I eventually did was different from Bubble’s instruction. I am just writing them here so if anyone experiences the same problem in the future can have a reference.
I was told by the Namecheap customer support that my account is set up incorrectly because there were 2 A records with @ and 2A records with www. and a URL redirect record. The customer service officer changed my setting to have two A records with wwww pointing to bubble’s IP address and a URL redirect record pointing mysite.com to www.mysite.com. Things seem to work properly now.

Big shoutout to @deadpoetnsp again for your help!

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