I need t know how "category" plays a role in how you work with your data. You've indicated that you have these relationships:
Table1::__pkTable1ID = Join::_fkTable1ID
Table2::__pkTable2ID = Join::_fkTable2ID
But what marks the missing records as part of a specific "category"?
Then, let's say your records are missing from Table2. Keep in mind that there are two ways to "view" that data from the context of a layout based on Table1:: You can set up a portal based on the join table or you can set up a portal based on Table2. Either way, Records from Table might not be visible in that context for several reasons: 1) Records in Table 2 have been deleted. If so, going to a layout based on Table 2, and performing finds/sorts, showing all records, etc will all fail to bring up these records. 2) The join table records have been deleted. In this case, you will be able to find records in table 2, but the missing join records makes them inaccessible from the Table1 layout. 3) the records in Table2 are there, but their pk values have been cleared or changed to break their link to the join records. This is probably very unlikely, but I can't rule out this possibility from here as I know only what you have posted about your database. 4) _fk fields (either one of the two such fields) have been cleared or changed.
I've had it happen more than once that redefining portal contents can be impossible to get to display correctly until the original field is deleted and reinserted.
If you are using FileMaker 12 or newer, I know of one issue that can be the cause of that problem. If you start having problems with how the portal displays data immediately after the layout's design has been modified, enter layout mode and move the portal a few pixels. The fields enclosed in the portal should move when the portal moves. If it doesn't, the portal no longer "owns" the field. It is just floating on top of the portal. Typically, this results in data only showing in this field in the first portal row. If this happens, drag the field completely outside the portal, release the mouse button and then drag it back, being caregul to keep all borders of the field totally inside the borders of the portal row.
Another way that you can encounter trouble is if you add a field to your portal from the correct table, but do so by selecting it from the wrong Tutorial: What are Table Occurrences?.
Thank you Phil. Very helpful. I was in fact missing the records from the join table and had to carefully inspect the 1600+ join records to see that. It was a new "category" that I was working to build the layout for, so I think I just hadn't inspected those particular records (done "QA") yet to discover the gaps.
I notice that my brain gets into quite a cramp when I tackle a new task and have to apply the framework of relational strategies. I get frustrated that I don't seem to be able to retain the "ah-ha" clarity that comes with getting previous strategies to work. So then I look at something new and think "I must know how to do this" or "this looks so familiar, but..." and when I find myself stumbling along I get a little freaked out, like suddenly "Oh god, I know nothing!" lol
It really is a labor of love to make these things work like they do.
And thank you for the pointers on altering fields in portals. Will be very helpful moving forward!