My mistake there is already a topic on this issue.
I was recently on my mobile device (iPhoneXS I believe) when I realized my username on the home page was different then my username on my actual profile page.
This bug I only started noticing today and only started happening after I changed my username 2 times on Desktop (Windows 10)
Here’s a video of this bug occurring,
This bug is easily reproducible by just exiting the Roblox iPhone application and re-entering it and then just seeing your username be different in two different locations.
Again my iPhone is the iPhone XS
Edit: I tried relogging into my iPhone Roblox application after signing out and this fixed the error.