Hello. Thank you for the detailed explanation. As you mentioned, I checked the Attributes inspector, but the Argument Number field is not visible.
I suspect that this field does not appear when a stringsdict has been migrated to xcstrings.
(For items generated by building code like LocalizedStringResource("key_1", defaultValue: "%lf %ld"), the Argument Number field does appear.)
Fortunately, I was able to resolve the issue by manually editing the JSON and adding the argNum field.
Alternatively, changing %arg to %2$ld also seems to fix the problem.
Is it intentional that the Argument Number field is not shown in certain situations?