I get a following problem after updating my moodle 3.3.1 to version 3.4.1
On the site there are some html - Blocks integrated.
The debugger tells me this:

Notice: block_html::specialization(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "object" of the object you are trying to operate on was loaded before unserialize() gets called or provide a __autoload() function to load the class definition in /srv/www/htdocs/moodle28/blocks/html/block_html.php on line 40

Notice: block_html::specialization(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "object" of the object you are trying to operate on was loaded before unserialize() gets called or provide a __autoload() function to load the class definition in /srv/www/htdocs/moodle28/blocks/html/block_html.php on line 40

Notice: block_html::specialization(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "object" of the object you are trying to operate on was loaded before unserialize() gets called or provide a __autoload() function to load the class definition in /srv/www/htdocs/moodle28/blocks/html/block_html.php on line 40

Notice: block_html::instance_can_be_docked(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "object" of the object you are trying to operate on was loaded before unserialize() gets called or provide a __autoload() function to load the class definition in /srv/www/htdocs/moodle28/blocks/html/block_html.php on line 152

Notice: block_html::get_content(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "object" of the object you are trying to operate on was loaded before unserialize() gets called or provide a __autoload() function to load the class definition in /srv/www/htdocs/moodle28/blocks/html/block_html.php on line 65

Notice: block_html::instance_can_be_docked(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "object" of the object you are trying to operate on was loaded before unserialize() gets called or provide a __autoload() function to load the class definition in /srv/www/htdocs/moodle28/blocks/html/block_html.php on line 152

Notice: block_html::instance_can_be_docked(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "object" of the object you are trying to operate on was loaded before unserialize() gets called or provide a __autoload() function to load the class definition in /srv/www/htdocs/moodle28/blocks/html/block_html.php on line 152

Notice: block_html::get_content(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "object" of the object you are trying to operate on was loaded before unserialize() gets called or provide a __autoload() function to load the class definition in /srv/www/htdocs/moodle28/blocks/html/block_html.php on line 65

Notice: block_html::instance_can_be_docked(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "object" of the object you are trying to operate on was loaded before unserialize() gets called or provide a __autoload() function to load the class definition in /srv/www/htdocs/moodle28/blocks/html/block_html.php on line 152

Notice: block_html::instance_can_be_docked(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "object" of the object you are trying to operate on was loaded before unserialize() gets called or provide a __autoload() function to load the class definition in /srv/www/htdocs/moodle28/blocks/html/block_html.php on line 152

Notice: block_html::get_content(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "object" of the object you are trying to operate on was loaded before unserialize() gets called or provide a __autoload() function to load the class definition in /srv/www/htdocs/moodle28/blocks/html/block_html.php on line 65

Notice: block_html::instance_can_be_docked(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "object" of the object you are trying to operate on was loaded before unserialize() gets called or provide a __autoload() function to load the class definition in /srv/www/htdocs/moodle28/blocks/html/block_html.php on line 152

Can anybody say what is happening there?
The Blocks are not shown on the webpage anymore.

Thanks
STefan