Here is what I think has been going down.
In Android, there is a security setting called "allow widgets on lock screen". The e-mail application can control this setting if it is set as administrator (which it will be if you are using activesync).
In a previous version, Sony looked at this and said "what shall we do with this setting if activesync requires a PIN-lock"? They decided that the email application should then disable lock-screen widgets, so that no one can see your messages etc on a locked phone. Note that activesync security policies say nothing about lock-screen widgets, so this is entirely up to Sony at this point.
Then the lollipop update comes. Lock screen widgets are gone, and replaced by lock screen notifications. Android (google, not sony) starts to interpret "disallow lock screen widgets" as "disallow lock screen notifications".
Meanwhile, Sony does nothing to the email application, but now, instead of preventing widgets, it prevents lock screen notifications. While the phone is usable without lock screen widgets, it becomes pretty much unusable without lock screen notifications.
Solution: Release an update to the Email application, where PIN-lock no longer automatically means no lock screen widgets.
(It could be the other way around though, that google interprets PIN-lock as no lock screen widgets, and Sony interprets no lock screen widgets as no lock screen notifications. In this case I suppose an update to the whole operating system is needed).
