Different initrd sizes between two Foreman instances -> Kernel Panic

Problem: Different initrd sizes between two Foreman instances

Expected outcome:Flawless provisioning

Foreman and Proxy versions:3.1.3

Foreman and Proxy plugin versions:

Distribution and version:Booth CentOS7

Other relevant data:

We have two Foreman instances in two seperate networks. The generated initrd is 53MB on one and 86MB on the other. New VMs which are tried to be provisioned on the Foreman instance that generates the bigger initrd files, fail with: kernel panic - not syncing: VFS: unable to mount root-fs on unknown block (2,0).

The VMs RAM is at 8GB, so there should be enough space for the ramdisk.
VMs that are beeing provisioned on the other instance work flawlessly.

What we tried so far is to copy the initrd and kernel from the working Foreman to the other instance by using the prior names under /var/lib/tftpboot/boot/, but without any success either.