I have a 2016 1533 and have only seen the temp one bar once. I was mowing tall broomweed in a bottom surrounded by woods and it was 102 out. I wonder if more than your tractor could be effected or is this specific issue on 25 series only.
A software update took care of this issue. Dash readout needed to be re-calibrated.
My 2015 Mahindra 1538 needed reflashed before temperature gauge even registered.
Like this ^