I can get the Shift-F1 to show the help for a user that has fish as login shell.
I get a glimpse of an error message that gets quickly overwritten.
fish: Variables may not be used as commands. Instead, define a function like 'function BYOBU_PAGER; sensible-pager $argv; end' or use the eval builtin instead, like 'eval $BYOBU_PAGER'. See the help section for the function command by typing 'help function'.
If I change the login shell back to
chsh then Shift-F1 will show the help page as expected.