I have tried to replicate what your picture shows but have been unable to. As I have not used chord symbols much, I don’t know if the following will help.
Do any other chords in the piece behave the same way? If so, then it looks like a setting might have been changed.
Have you changed anything in Engraving Options > Chords? There is a huge number of variations in appearance, position, etc. to choose from.
Have you changed any of the font/character styles, particularly those relating to chords? To check and/or experiment, go into Engrave mode and choose the Engrave menu from the top menu bar. The first few menu items relate to fonts and styles.
As I have not experienced this behaviour myself, I am unsure of anything else to suggest. There are other regular contributors to this forum who have vastly more experience with Dorico than I do. Hopefully they will be able to suggest other things to try.
(A few minutes later) -
Further to my second suggestion, I chose Engrave > Font Styles… , and in the Edit Font Styles window, chose Chord Symbols Music Text Font and changed the Font family from Bravura Text to Academico. This had the effect of removing the flat symbol and the slash mark between the letters. One visual difference which I noticed is that the space between them was much less than in your picture. So it might not be the complete solution, but it could be a good place to start.