I’ve seen something similar just now using a different UTM projection
This can happen if
- You set the grid to match your UTM - EPSG:32648
- You use format “Decimal with suffix”
- You used “cm” or “mm” as the interval units
I think the last one might be the problem. All the coordinates are positive, and start in the bottom left.
Note that “mm” and “cm” refer to the print size, not real world units, so will vary according to scale.
You can also get odd results mixing degrees formatting with a UTM grid.
Here's an example showing the same results:-
If you want the grid to be in degrees, use WGS84 for your grid. If you want it to be in meters, to match the UTM coordinates, use the UTM projection and set the format to “Decimal”
What you can’t do, unfortunately, is specify a map interval of “degrees” on a UTM grid - just map units (always meters for UTM), cm or mm.