Sadly you have encountered the main issue with dynamic fields. I forgot that reorganize not only allows you to edit your DBs on another device, but it tells Ninox to do sort of reset record Ids. That is why I do not use dynamic fields as storage but only as a UI element. All of my dynamic field selections are written to a table. I've only seen this happen with dynamic fields that come from tables where you only grab a subset of records that change constantly. And only when you delete groups of records from the root table.

This is how I think about this issue. In my DB, I track show jumping results. I track the rails that are knocked down by each rider and horse. So there is a different order of jumps for each event, and some even have two different set of jumps. For event1, records 1 - 10 from the course table are displayed in the dynamic choice for each rider. So then I select from those 10 records. Then event2, records 11 - 20 are related. For event3, I create records 21-30, but make a mistake and I end up deleting 26-30 and add 31-35, so I have 10 jumps. So for event3, records 21-25 and 31-35 are related. Then for a rider I mark records 32 and 33 as being knocked down.

Now I reorganize the DB. Ninox will reorganize the record IDs of the course table so they are now sequential 1 - 30. But the record for the rider still has it down as records 32 and 33, so it will show nothing. But if you did numbers(multidynamicfield), it will show you the Ids of the actual selection.

If you have root table that is simple or never sees any deletes then you should never see this issue.