Missing character: There is no  (U+007F) in font dsrom10!
Missing character: There is no  (U+007F) in font dsrom10!
.....
Missing character: There is no  (U+007F) in font dsrom8!
Missing character: There is no  (U+007F) in font dsrom8!
.....

documentclass{article}
usepackage{amsmath}
usepackage{dsfont}
begin{document}
begin{equation}
hat{bar{mathds{H}}}
end{equation}
end{document}

...
setboxz@hbox{$#1#2@empty{}macc@skewchar$}%
setboxtw@hbox{$#1#2@emptymacc@skewchar$}%
...

defmacc@a#1#2{%
  ...
  setboxz@hbox{$#1{#2}@empty{}macc@skewchar$}%
  setboxtw@hbox{$#1{#2}@emptymacc@skewchar$}%
  ...
  }

defmmacc@nested@a#1#2#3#4#5{%
  ...
  macc@palettemacc@a{{#5}}%
}