It's never "everyone" but I do recall Mane getting a significant amount of flak in his early days. Would be surprised if it wasn't the majority view at the time.
I think the most concerning element of Lyanco's debut for me is that his mistake for their second goal was a completely unforced error. You could understand such a woeful pass if the player was under pressure, but he wasn't. Maybe it was a one off brain-fart and one's concern is unfounded. Who knows. I'm usually one of the last people on here to make snap judgements about managers, players, early season form, etc, so I'll give Lyanco the benefit of the doubt despite these initial concerns.