Roblox is banned in my country, and I’ve been accessing it with a “public” VPN for months. I haven’t encountered any of these issues, can’t reproduce at all.
Are you using a free or common VPN service? The 429 error code response is served when a client is making too many requests. If you are using a free or commonly used VPN multiple people could be accessing these endpoints leading to it having a lot of requests made from the same IP.
I’ve heard people experiencing similar rate-limiting issues with paid VPN services too. I believe Roblox has some internal mechanism that can differentiate legitimate IP addresses to those of VPN users, and probably heavily throttles the amount of requests a VPN user can make before getting rate-limited.
It’s possible, but the more likely reason I’m asuming is that people who bot games and the like are using paid VPN services. If you want a super secure VPN experience that guarantees you won’t run into this proble, you can actually set up your own VPN server on a remote computer using DigitalOcean or another provider in a specific area and connect to that. Though I would excercise caution in regards to this as some providers charge based on traffic and data usage rather than a set amount for a timeframe.