This is one of the reasons its frustrating to have multiple duplicate topics.
No the actual issue is that flathub has problems.
And another issue is that arch-update does not check or fail gracefully.
And also that arch-update looks at flathub at all even if the system has no flatpaks.
I have no idea if this is ever going to be ‘fixed’ or when or in what fashion. But until then or the connection becomes healthy or you apply that option (which apparently everyone should apply anyways unless using flatpak - to save time,cpu,energy,etc if arch-update is going to be a little dumb) it would seem to have a pretty sizable impact on the usability of this tool.
Maybe it will just encourage you and others to use
pacmanas the Archangels intended.