@email@example.com @CryptGoat - from my POV Monal on IOS works well, even with OMEMO. There has been lots of work lately on Monal for IOS, so when you tested it 3 months ago it might be that your issue has been solved in the meantime.
This doesn't mean that there aren't any issues anymore in Monal, but it is usuable and for me it has less battery drain than ChatSecure.
You can as well help with Monal by reporting issues to the author, of course.
@erlequin @CryptGoat @firstname.lastname@example.org - Does CS use the Apple Push Notification Service? Monal does. When CS does not it needs to poll. Maybe not now, but when Apple tighten the rope around your neck to force you to use APNS (with IOS 13).
I don't think there is a (huge) delay in Monal, but I mostly use XMPP on desktop devices, although I administer thousands of mobile devices with Cisco Jabber at my day job.
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