Given from what I can see in fm's bitbucket repository commit history for newLiquidCrystal,
the default pin mapping used in the LiquidCrystal_I2C class has never changed.
Also, no changes or updates to the IDE would alter this.
The only way a newLiquidCrystal library from fm's bitbucket site could work with the stated backpack,
is if it had been modified.
So my conclusion is that the code that previously worked with the stated h/w had been modified.
It either cam from a different source that fm's bitbucket site (where it had been modified), or it was modified locally.
And then when the library was updated, these modifications to the default pin mappings were lost.
--- bill