This might be a kernel bug. What version of IPFire are you running?
These messages seem to be related as the AMD-Vi one I have found linked to iommu. In CU169 or CU170 there were new kernels which did appear to have iommu bugs in them with some hardware that was raised in the community. However since the updated kernel version in CU171 I haven’t seen any more reports about kernel issues except for yours and one other. That other one did not have any info on what the kernel message was and his symptoms are quite different from yours.
https://community.ipfire.org/t/green-no-internet-on-171/8976
Looking up the above messages some people added iommu=off or iommu=soft on the grub kernel cmdline but that was on desktop computers not IPFire.