Fatal error when activate AT Theme Generator

Hi!
First of all I want to thank author of AdaptiveTheme - mr. Jeff Burns (I hope he is ok! :-/ ), and also mr.Matt Bloomfield for all their huge effort for this great Theme!

Problem

Here's the problem I came across.
I have some trouble with AT Tool 2.0 (or something else associated with “at_theme_generator”).
When I want to install/activate submodul “AT Theme Generator” I got Fatal error:

"Fatal error: require(): Failed opening required '/public_html/modules/contrib/at_tools/at_theme_generator/src/Form/GeneratorForm.php' (include_path='/public_html/vendor/pear/archive_tar:/public_html/vendor/pear/console_getopt:/public_html/vendor/pear/pear-core-minimal/src:/public_html/vendor/pear/pear_exception:.:/usr/share/php') in /public_html/vendor/symfony/class-loader/ApcClassLoader.php on line 112"

Also in logs I found some logs:
"User warning: The following theme is missing from the file system: at_generator in drupal_get_filename() (line 295 of /public_html/core/includes/bootstrap.inc"

Steps to reproduce

A more detailed description:
On local Drupal 8.9.19 site (on local LAMP: Apache 2.4.38 (Debian), PHP 7.3.29-1, MariaDB 5.5.5-10.3.31) I have latest original Adaptive Theme (8.x-3.1) and AT Tools (8.x-3.3 (D9 compatibile)), with my AT Subtheme and all is fine.
Because I must update site to D9 (asap :-/ ), before go to new other D9 compatible theme, a was going to try recomended solution with AT Theme 2.0.
I follow the tutorial: https://www.drupal.org/files/Adaptive%20Themes%20for%20D9%20translation.pdf → (only I go manualy, without Composer).
First all is fine (I make other theme (my W3CSS subtheme) default theme, uninstall old AT Tools (module+submodule), remove from site files of AdaptiveTheme and AT Tools, (with flush all cache in process), ekstract new files for AT Theme 2.0 and AT Tool 2.0).
Also I was able to install/activate first modul "AT Tool" without problem!
But when I try to install/activate "AT Theme Generator" submodul - I got this error:
"Fatal error: require(): Failed opening required '/public_html/modules/contrib/at_tools/at_theme_generator/src/Form/GeneratorForm.php' (include_path='/public_html/vendor/pear/archive_tar:/public_html/vendor/pear/console_getopt:/public_html/vendor/pear/pear-core-minimal/src:/public_html/vendor/pear/pear_exception:.:/usr/share/php') in /public_html/vendor/symfony/class-loader/ApcClassLoader.php on line 112"

And stuck with that. :-/
Flush all cache (in AdminToolbar menu from other opened tab) not helping, Run cron not helping.
Surprisingly, but when I make a small break and sudenli I got Home page running!
But when I tried to open some other page - I got same error. :-/

Proposed resolution

PS
I'm not programer so sorry for not much help - I know about your problems and care to hold this project I live - I just hope that reporting a perceived problem will help to improve the project.

Remaining tasks

User interface changes

API changes

Data model changes