based on your phrasing, your print isn't changing temperature, your nozzle temperature is dropping. The "40-50 percent" reference is also ambiguous, but let's run with the nozzle first.

Check your slicer settings to determine that it's not commanding a temperature change at a specific layer.

You can also examine the g-code file by opening it in a text editor (notepad or similar) and searching for the lines for temp. The code will begin with M104 and may have the letter S followed by a number (bed temp) and/or the letter T with a zero followed by a number (nozzle temp).

Those lines should appear only near the beginning of the print and set to zero at the end of the print. If you find an M104 code in the middle of the file, check for a Z reference, to determine layer height, then check your slicer settings to ensure or remove that setting from the build.

Consider also to attach your g-code file to the message if you aren't sure where to look.