IDP sending empty SignatureValue in ArtifactResponse

[Malo Toudic]

Hello,

We are running Shibboleth IDP 3.3.2 and have encountered a problem 
responding to SP.
We have registered multiple SP metadata in our IDP and one of them is 
getting a strange response to its artifact Requests.
The signature of the ArtifactResponse indeed has an empty value. The 
rest of the signature seems fine, but the value is empty. Some other SP 
using same Signature Method are receiving normal responses with 
SignatureValue filled.
We investigated our configuration as well as SP's metadata and have not 
found the source of this problem.
The logs are also not showing any error or warning that could 
explain/relate to this problem.

Thanks in advance for your responses,

Regards,

Malo Toudic