Some files have not passed the integrity check. Upgrade to 28.0.4 mail app

Just did the upgrade to 28.0.4 and now this appears in the Security & setup warnings: Some files have not passed the integrity check.

EXTRA_FILE. Is the signature.json not up to date, or are there obsolete files?

Any help is much appreciated!

Technical information
=====================
The following list covers which files have failed the integrity check. Please read
the previous linked documentation to learn more about the errors and how to fix
them.

Results
=======
- mail
	- EXTRA_FILE
		- vendor/ezyang/htmlpurifier/library/HTMLPurifier/DefinitionCache/Serializer/URI/4.15.0,3478238e680361cd87bf880f5b3cc50a1e7abc6c,1.ser
		- vendor/ezyang/htmlpurifier/library/HTMLPurifier/DefinitionCache/Serializer/HTML/4.15.0,100a0d442686872045400b774dcb082c945a1908,2019080701.ser

Raw output
==========
Array
(
    [mail] => Array
        (
            [EXTRA_FILE] => Array
                (
                    [vendor/ezyang/htmlpurifier/library/HTMLPurifier/DefinitionCache/Serializer/URI/4.15.0,3478238e680361cd87bf880f5b3cc50a1e7abc6c,1.ser] => Array
                        (
                            [expected] => 
                            [current] => 403272903ab6fd6acf8073eff7d4449d1d3c14a96ea299c257a66b334e44b09b0554c4f3be88a269f233dc1ec7e077e739d7a6d2c744dc9e1dadd7757ed1ca09
                        )

                    [vendor/ezyang/htmlpurifier/library/HTMLPurifier/DefinitionCache/Serializer/HTML/4.15.0,100a0d442686872045400b774dcb082c945a1908,2019080701.ser] => Array
                        (
                            [expected] => 
                            [current] => c68d95b7adc0174b7dcdc500b4480d4e29378ecda31c124be014323035795d47678e4d77629e7cfc8a667f6ec49863274ee48654b0a93d18e3a20c9f0febcdbf
                        )

                )

        )

)

linux 6.1.0-18-amd64 on debian 12.5
php8.1
nginx
postgres

According to the documentation, both “EXTRA_FILE” can be removed. After doing so and executing a rescan, the files re-appear and the error message in the administration settings remains.

The mail app was updated today to version 3.5.8 but this didn’t solve this error.

What else can be done?