The D flag is typically seen when the AP is booting up initially, or has rebooted very recently.
The I flag means inactive. You typically see this when the configuration means no "real" services are active on the radios. There could be lots of reasons why. For example, the config is deliberately or dynamically causing the radios to be in this state. Or, the AP could have recently rebooted. Or (unlikely) you've got a bug.
To start us off, on the APs where it happens, is it like that all the time, or does it come and go?
Check if the APs in question are rebooting (show ap debug counters), looking at the reboot column.
If nothing there, we'll need to see your config, and an output of "show ap database long".
Thanks.