Codebuild: Adding multiple EFS suddenly failes

We have been successfully using codebuild with multiple EFS mounts in the past. Since ~3 days mounting more than one EFS appears to silently fail.

Within the AWS console the EFS's all report to be available and Codebuild also lists these as mounted. However, running a ls on the mount-points within the codebuild instance itself reveals that only one of these mounts show up.

Removing this successfully mounted EFS from the codebuild configuration and rerunning the project will then mount the next EFS (I assume in alphabetic order), however mounting any additional EFS mounts will still fail.

We tried recreating the codebuild project and (one) of the offending volumes, without any luck so far.