Documentation on hover doesn't show up for functions which use shortened method syntax (-preview=shortenedMethods).
E.g. in the following code documentation on hover works for fun(), but not for gun():
import std.stdio;
/// Comment
int fun() {return 13;}
/// Other comment
int gun() => 42;
void main()
{
writeln(gun());
writeln(fun());
}
Serve-d log file
code-d: 0.23.2
serve-d: 0.7.4
dcd: 0.13.6