Keybinding C-M-a for LaTeX-find-matching-begin does not work!

[Heiko Schröder]

Dear list,

it is said, that C-M-a is bound to LaTeX-find-matching-begin. And it 
should move to the \begin of the environment.

But that is not true.  It does NOTHING.

In contrast to that:  C-M-e works fine.  Even it not possible to bind 
C-M-a explicitly to LaTeX-find-matching-begin over .emacs.

LaTeX-find-matching-begin alone works rather fine.

But there sometimes is the message:  ,,Can't find begin of 
environment'', which is ridiculous.

It seems to be a rather severe bug in AUCTeX.

I use Emacs Version 26.3 with AUCTeX 13.1.


Regards

Heiko Schröder