XMPP is more reliable than Signal on iOS. My wife regularly doesn't get Signal notifications for messages that I sent when she was in a marginal service until hours later when she opens the Signal app to send me something.
On Android, I've never had any connection issues with either Signal or XMPP, so I would say that this problem is solved.
On Android, I've never had any connection issues with either Signal or XMPP, so I would say that this problem is solved.