So your mechanical leader and notes are behaving badly and not scaling to the viewport scale. Bad notes, bad... You either need the notes whisperer or set a couple of variables to neuter these issues. AMSYMSCALE sets symbols (ie Notes) back on track and AMRESCALE gets your existing notes to behave. Whew.. good notes, good.
Or should I say "that isn't special". The special characters in the dimensioning mode show incorrectly. The diameter symbol for instance looks like some weird text. Well this is a Window Font issue. Look for the AMGDT*.ttf fonts in the Windows\Font folder. If they are not there, copy them from a working computer or do a repair install of AutoCAD Mechanical and you should get them back. Congratulations, you are special again.