We have had this issue before and 99% certain hat its just a setting issue, what you need to do is reset your font cache on the OSD chip… do that you need to do the following:
- Plug the Lipo
- Plug the flight controller to a configurator (Betaflight)
- Go to OSD tab
- Click on « Font Manager » in the bottom write corner
- Select the desired Font and click « Upload Font »
Once you have tried that it should display correctly 
Update: IF you still have the same issue after updating the fonts, make sure the FC is powered via Lipo, as sometimes the USB cant provide enough power for the OSD module.