Connecting PJ Excange to iPhone?

Question

iOS

Colleagues, there are a couple of questions about connecting Excange PJ to iPhone:
1) There was a change of the Wildcard certificate to Exchange - everything worked properly, tel. On Androyd, mail is received normally, on iPhone they are received normally only if you use Outlook for iOS. There are problems with the built-in mail client - sometimes it works, sometimes the error "Incorrect UZ" occurs. Those. It works for three days, then falls into an error, does not work for a while, then starts working without any third-party intervention. I can’t figure out which way to dig, what logs and settings to look at, and where?
2) If suddenly this is connected somehow with certificates, then how to fix it? Do I need to install a certificate on iPhone? How to do it? And why is everything ok on Android + in Outlook for iOS?
The problem is not massive, but unpleasant. With US everything is ok.