Cannot use mapping to lua functions

[nikonakoneko]

If I use vim.keymap.set and pass a lua function as rhs like this:

vim.keymap.set('n', '<Leader>cc', function()
    return vim.v.count == 0 and '<Plug>(comment_toggle_current_linewise)' or '<Plug>(comment_toggle_linewise_count)'
end, { expr = true })

I get the following error on opening leader guide:

Error detected while processing function leaderGuide#start_by_prefix[12]..<SNR>17_start_parser:
line   11:
E716: Key not present in Dictionary: "lhs =~ '<Plug>.*' || mapd.lhs =~ '<SNR>.*'"
line 12:       continue
line 13:     endif
line 14:     let mapd.display = s:format_displaystring(mapd.rhs)
line   14:
E716: Key not present in Dictionary: "rhs)"
E116: Invalid arguments for function s:format_displaystring
line 15:     let mapd.lhs = substitute(mapd.lhs, key, "", "")
line   15:
E716: Key not present in Dictionary: "lhs, key, "", "")"
E116: Invalid arguments for function substitute
line 16:     let mapd.lhs = substitute(mapd.lhs, "<Space>", " ", "g")
line   16:
E716: Key not present in Dictionary: "lhs, "<Space>", " ", "g")"
E116: Invalid arguments for function substitute
line 17:     let mapd.lhs = substitute(mapd.lhs, "<Tab>", "<C-I>", "g")
line   17:
E716: Key not present in Dictionary: "lhs, "<Tab>", "<C-I>", "g")"
E116: Invalid arguments for function substitute
line 18:     let mapd.rhs = substitute(mapd.rhs, "<SID>", "<SNR>".mapd['sid']."_", "g")
line   18:
E716: Key not present in Dictionary: "rhs, "<SID>", "<SNR>".mapd['sid']."_", "g")"
E116: Invalid arguments for function substitute
line 19:     if mapd.lhs != '' && mapd.display !~# 'LeaderGuide.*'
line   19:
E716: Key not present in Dictionary: "lhs != '' && mapd.display !~# 'LeaderGuide.*'"
line 20:       if (visual && match(mapd.mode, "[vx ]") >= 0) || (!visual && match(mapd.mode, "[vx]") == -1)
line 22:         let mapd.lhs = s:string_to_keys(mapd.lhs)
line 23:         call s:add_map_to_dict(mapd, 0, a:dict)
line 24:       endif
line 25:     endif
line 26:   endfor
line 9:   for line in lines
line 10:     let mapd = maparg(split(line[3:])[0], line[0], 0, 1)
line 11:     if mapd.lhs =~ '<Plug>.*' || mapd.lhs =~ '<SNR>.*'
line   11:
E716: Key not present in Dictionary: "lhs =~ '<Plug>.*' || mapd.lhs =~ '<SNR>.*'"
line 12:       continue
line 13:     endif
line 14:     let mapd.display = s:format_displaystring(mapd.rhs)
line   14:
E716: Key not present in Dictionary: "rhs)"
E116: Invalid arguments for function s:format_displaystring
line 15:     let mapd.lhs = substitute(mapd.lhs, key, "", "")
line   15:
E716: Key not present in Dictionary: "lhs, key, "", "")"
E116: Invalid arguments for function substitute
line 16:     let mapd.lhs = substitute(mapd.lhs, "<Space>", " ", "g")
line   16:
E716: Key not present in Dictionary: "lhs, "<Space>", " ", "g")"
E116: Invalid arguments for function substitute
line 17:     let mapd.lhs = substitute(mapd.lhs, "<Tab>", "<C-I>", "g")
line   17:
E716: Key not present in Dictionary: "lhs, "<Tab>", "<C-I>", "g")"
E116: Invalid arguments for function substitute
line 18:     let mapd.rhs = substitute(mapd.rhs, "<SID>", "<SNR>".mapd['sid']."_", "g")
line   18:
E716: Key not present in Dictionary: "rhs, "<SID>", "<SNR>".mapd['sid']."_", "g")"
E116: Invalid arguments for function substitute
line 19:     if mapd.lhs != '' && mapd.display !~# 'LeaderGuide.*'
line   19:
E716: Key not present in Dictionary: "lhs != '' && mapd.display !~# 'LeaderGuide.*'"
line 20:       if (visual && match(mapd.mode, "[vx ]") >= 0) || (!visual && match(mapd.mode, "[vx]") == -1)
line 22:         let mapd.lhs = s:string_to_keys(mapd.lhs)
line 23:         call s:add_map_to_dict(mapd, 0, a:dict)
line 24:       endif
line 25:     endif
line 26:   endfor
line 9:   for line in lines
line 10:     let mapd = maparg(split(line[3:])[0], line[0], 0, 1)
line   10:
E684: list index out of range: 0
E116: Invalid arguments for function maparg
line 11:     if mapd.lhs =~ '<Plug>.*' || mapd.lhs =~ '<SNR>.*'
line   11:
E716: Key not present in Dictionary: "lhs =~ '<Plug>.*' || mapd.lhs =~ '<SNR>.*'"
line 12:       continue
line 13:     endif
line 14:     let mapd.display = s:format_displaystring(mapd.rhs)
line   14:
E716: Key not present in Dictionary: "rhs)"
E116: Invalid arguments for function s:format_displaystring
line 15:     let mapd.lhs = substitute(mapd.lhs, key, "", "")
line   15:
E716: Key not present in Dictionary: "lhs, key, "", "")"
E116: Invalid arguments for function substitute
line 16:     let mapd.lhs = substitute(mapd.lhs, "<Space>", " ", "g")
line   16:
E716: Key not present in Dictionary: "lhs, "<Space>", " ", "g")"
function leaderGuide#start_by_prefix[12]..<SNR>17_start_parser aborted

continuing in function leaderGuide#start_by_prefix

function leaderGuide#start_by_prefix aborted