A system update of Redhat 7, and related updates to CentOS, included a version of ImageMagick with a bug in black and white image production. UnForm was configured to use a -type BiLevel or -monochrome option, which at ImageMagick 6.7.8-9 2019-02-01 started failing. You can test the version with this command line: convert --version.
A workaround was found by changing the '-type Bilevel' or -monochrome options to this sequence to '-type grayscale -threshold 50% -colors 2'. If your version of UnForm is affected by this Magick version, and is configured to use the former option, you can change this in the field. To do so, locate the live bmp1= line in the [images] section of uf90d.ini or uf100d.ini. Remove -monochrome or '-type BiLevel' options, and add '-type grayscale -threshold 50% -colors 2' before the output file name value, "BMP3:%o".
After this change, you might need to clear the image cache, where converted images are stored for reuse. To do so, just remove the images.dat file from the UnForm directory. The file will get recreated and rebuilt as needed.