When you have an item with a DEADLINE that includes both a repeater and a special warning period, such as DEADLINE: <2018-12-31 Mon 09:00 +1w -1d>, it seems to not be detected as a timestamp. Such items will not appear in the agenda view at all, and will appear in the TODO view, when you filter by "No Dates".
Currently the special warning periods are not supported. A repeater however should be recognized and used for displaying tasks in the agenda.
The next update to beorg will handle a repeater in that the state will be reset to TODO (i.e. the first todo action state, or the value of org-todo-repeat-to-state) and the date correctly updated based on the repeater type. There will also be a UI to create and modify repeaters for dates.
In response to the above messages, my report here is not about repeater functionality. It's about timestamps that have a special warning period not being recognized as timestamps at all.
Likewise, timestamps such as <2019-01-07 Mon +30d/90d>, typically used with org-habit, are not recognized. Items scheduled in this way don't show in the agenda view, and do show in the TODO view with the "No dates" filter, contrary to user expectation.
I think it would be important to first have these recognized as just regular timestamps, even if ignoring any special warning periods, habit windows or repeaters, just so that any existing timestamps that I have created via emacs are interpreted correctly on beorg.
I'll look at adding support (in addition to special warning periods) for org-habit like timestamps in a future update. Is anyone aware of any additional timestamp formats for which it would be useful to also have support?
I just read in the manual (https://beorgapp.com/manual/) that "When a repeated task is marked as done beorg will change the date to when it should next be completed."
Also, a bit further: "To set a date to repeat:Tap the Repeat… button at the bottom of the date dialog."
None of these features seem to appear in the current release of beorg. I assume the manual is ahead of the released version?
Sorry for it taking a while for your comment to be approved - I'm new to this particular forum software and not quite sure how it selects which comments require moderation.
The latest beorg on the App Store now supports this feature as described in the manual. I updated the manual prior to the app update being approved.
You should find that beorg understands ranges such as...
<2018-12-31 Mon 09:00-10:00>
<2018-12-31 Mon>--<2018-01-05 Sat>
... and should display these as expected in the agenda.
Currently there isn't a specific UI for editing these - that is in my list of things to implement. You can edit these manually, either in the item notes or when editing the plain text of a file in beorg.