I have now found a solution myself and thought I'd let you know:
The function is unchanged but I simply reapply the appropriate autocommands
to the next buffer. That means I chanched above autocmd to read
autocmd VimEnter * if LucCheckIfBufferIsNew(1) | bwipeout 1 |
\ doautocmd BufRead,BufNewFile | endif
For my usecase I can say this is solved but if anyone of you knows a
nicer solution I'll still be happy to hear about it.
Lucas