Problems with running 2 instances with local APCu

Nextcloud version: 26.0.1
Operating system and version: Ubuntu 20.04.6 LTS
Apache or nginx version: Apache 2.4.41
PHP version: 8.1

Using an LAMP-server with 2 instances of Nextcloud (no docker, just 2 domains), I faced an error 500 after updating both instances to 26.0 (and 26.0.1 doesn’t change anything). I’m using

'memcache.local' => '\\OC\\Memcache\APCu'

I debugged the problem and realized, that the ClassLoader is getting the wrong file path and then PHP tries to include a file located in the path of the other instance. In detail the instance who first wins adds it’s path to apcu and apcu_fetch always returns that path, even to the other instance. For one instance it’s fine, the other one fails due to open_basedir restriction.

I fixed it by changing the APCu-Prefix for one of the two instances in ./lib/base.php:601.

I didn’t find a way to change the prefix in config.
So is this a bug or am I doing something wrong? Do I need to configure APCu different?

They have a patch for this problem already:

and the original bug report:

Thanks and sorry for reopening that, didn’t find that. So I wait for 26.0.2.