I have just verified something which I have suspected for a long time. I have two tables in my solution with many fields named identically. The solution allows time slots for a school timetable to be altered in one table, then all records in the other table to be deleted and replaced through a field import.
The field mapping was originally set up by "matching field names". I then unticked a field, which changes the mapping to "custom import order". After a save and revisit, it's set to "last order". That's all OK and expected.
All was well while everything was left alone, but then I did some culling of unused fields in the destination table. To my horror, the field mapping is thrown out.
The attached file "before-field-deletion" shows everything lining up. I then deleted the field "Minutes" in the destination table. "after-field-deletion" shows that every field below the missing "Minutes" field has been moved up in the import map.
I thought this issue, or something similar (non-importing of new fields) was addressed in FMP12, but this behaviour is just as damaging. Luckily my clients (in another country) haven't been exposed to the consequences, as I have discovered the behaviour first. I am now combing through the solution to find the hundreds of import scripts lurking in there and using a different technique to transfer records.
FMPA 16.03, MacOS Sierra, MacBook Pro