Just a similar issue some new LCD s arrived and swapped them into an existing working Sketch and got nothing
I was using "0x27" so tried "0x3F" and I got back light, good start. Then turned the little pot (Contrast) on the back a bongo, text. All good.
LiquidCrystal_I2C lcd(0x27,2,1,0,4,5,6,7,3,POSITIVE); // Set the LCD I2C address
LiquidCrystal_I2C lcd(0x3F,2,1,0,4,5,6,7,3,POSITIVE); // Set the LCD I2C address