I don't know which font u have used, but all the fonts that are available has problem with letters that have "islands" (i don't know how to phrase it).
A B D O P Q R
a b d e g o p q
Needs to find a font that connect the inner part of the letter so it would be printable.
Unfortunately, I know about this problem, but I couldn't find a font that has bridges and is supported by OpenSCad and Makerworld. If you know of such a font, please let me know. :)