I've discussed about this in the past but we never came out to a consensus on what was causing it.
Recently I had a couple of friends experiencing the same issue, so I wanted to see if others experienced it and if a cause was ever found.
Description:
Sometimes whole macrolines disappear. When that happens, it's the whole line, all 20 macros (10 alt + 10 ctrl) in that line.
I've seen it happen on the slot 0, sometimes on other slots. If there's a pattern on which slots are more likely to disappear, I didn't notice one.
It doesn't happen in all of my macro books, but only in some.
Odd occurrence:
When this problem happens, if I try to download the macroset (working, with all lines okay) from the FFXI server which I uploaded weeks before, the download happens but the disappeared macro lines do not re-appear.
Solution?
The only solution I found so far is using the FFXI backup in-game data tool. Backupping the whole FFXI/user folder might work as well but I never tried.
If I restore a saved set of settings with the official config app, then all my lost macro-lines are correctly restored.
Possible causes?
I never understood what causes this, but my feeling is that it has something to do with the very very few times when I dualbox logging a friend's char.
When that happens I usually logout the friend's char before mine (and everything works) and later, when I logout my own char, I get back to Windows 10 with a black/stuck POL window that's supposed to disappear but instead stays there permanently and I have to close it manually.
This always happens 100% of the times I log a second character and logout the other char before my own.
I'm not sure this is what's causing the macro-line disappearence but I have a feeling it's somehow related.