It did happen once for me. From what I understand, there cannot be more handles opened to the mcu::HWC service, and if attempted to get handle while already taken it blocks until it is free. Rosalina pauses any running app (home menu in this case), so the handle will never be freed and it...
I'm not sure, I think the font does not have it, as weird as it may be.
% is not the only character that will not be printed there, also some ascii chars ("b", "B", ...). Yes, I did try %%, no effect.
Currently there are 2 patches (EU only):
Battery percent in status bar (statusbatpercent)
This patch replaces date in statusbar with battery percent. It is not possible to display "%" character, so it shows battery percent as ":35:" instead.
Battery icon in status bar with 25% bars...