Hope you are doing well and sorry for the trouble. As described, when using fill and sign the text appears to be whit or transparent and you want to change it.
Would you mind sharing the version of the Adobe Acrobat Reader DC you are using? To check the version go to Help > About Acrobat and make sure you have the latest version 20.13.20074 installed. Go to Help > Check for Updates and reboot the computer once.