emacs 30.5.0 editing epub

[H . -J . Heitländer]

Hi there,

trying to get my feet wet with emacs and lisp. ... well it seems I am 
drowning...

The problem:

I am editing epub archives and  any saves that I am doing result in

<snip>

***backtrace***

Debugger entered--Lisp error: (wrong-type-argument stringp nil)

doc-view--revert-buffer(#f(compiled-function (&rest args) #<bytecode 
-0x1d096aa50772e2b6>) t t)

apply(doc-view--revert-buffer #f(compiled-function (&rest args) 
#<bytecode -0x1d096aa50772e2b6>) (t t))

#f(advice doc-view--revert-buffer :around #f(compiled-function (&rest 
args) #<bytecode -0x1d096aa50772e2b6>))(t t)

archive--mode-revert(#f(advice doc-view--revert-buffer :around 
#f(compiled-function (&rest args) #<bytecode -0x1d096aa50772e2b6>)) nil nil)

apply(archive--mode-revert #f(advice doc-view--revert-buffer :around 
#f(compiled-function (&rest args) #<bytecode -0x1d096aa50772e2b6>)) (nil 
nil))

#f(advice archive--mode-revert :around #f(advice doc-view--revert-buffer 
:around #f(compiled-function (&rest args) #<bytecode 
-0x1d096aa50772e2b6>)))(nil nil)

revert-buffer()

archive-write-file-member()

run-hook-with-args-until-success(archive-write-file-member)

basic-save-buffer(t)

save-buffer(1)

funcall-interactively(save-buffer 1)

command-execute(save-buffer)

</snip>


For the moment I can live with that as in reality the epub is being saved.

My problem is that from that moment on the display of the epub subfile 
(<name>.html) loses the utf-8 display. (oh, and every other file is 
being displayed in the same - wrong - way.)

The content is shown as (example)

<snip>

\342\200\234Nicely done. Now let\342\200\231s get that equipment on 
board.\342\200\234 </p>

</snip>

It should have been shown as

<snip>

"Nicely done. Now let's get that equipment on board." </p>

</snip>

I searched the internet without any result. Don't know which part of 
documentation to read.

Question: How do I switch the display back to show the contents in the 
expected way???


TX

Heiner