Collabora Docker - 'su: system error' during Docker start generating keys

I’m using nextcloud on a Synology NAS and would like use collabora to. During the start of collabora with Docker I get the following informations:

Generating RSA private key, 2048 bit long modulus
…+++
…+++
e is 65537 (0x10001)
Signature ok
subject=/C=DE/ST=BW/L=Stuttgart/O=Dummy Authority/CN=localhost
Getting CA Private Key
su: System error
Generating RSA private key, 2048 bit long modulus
…+++
…+++
e is 65537 (0x10001)
Generating RSA private key, 2048 bit long modulus
…+++
…+++
e is 65537 (0x10001)
Signature ok
subject=/C=DE/ST=BW/L=Stuttgart/O=Dummy Authority/CN=localhost
Getting CA Private Key
su: System error
Generating RSA private key, 2048 bit long modulus
…+++
…+++
e is 65537 (0x10001)
Generating RSA private key, 2048 bit long modulus
…+++
…+++
e is 65537 (0x10001)
Signature ok
subject=/C=DE/ST=BW/L=Stuttgart/O=Dummy Authority/CN=localhost
Getting CA Private Key
su: System error
Generating RSA private key, 2048 bit long modulus
…+++
…+++
e is 65537 (0x10001)
Generating RSA private key, 2048 bit long modulus
…+++
…+++
e is 65537 (0x10001)
Signature ok
subject=/C=DE/ST=BW/L=Stuttgart/O=Dummy Authority/CN=localhost
Getting CA Private Key
su: System error

It looks like, that there are missing rights during the generation of the keys. Has anybody running nextcloud and collabora on a Synology NAS and has a hint for me?