Hi @skeyby,
We recently had to adjust our CAA checking implementation to handle CNAMEs differently. As part of that we added a threshold for the maximum number of CNAME dereferences we would follow. Another user opened a Boulder bug about this limit being too low.
It does seem like in your case the limit is being reached without successive CNAMEs and I suspect there may be a bug in the implementation. I recommend you follow Issue #3093 while we get to the bottom of the problem.
Update: This was not a bug, the user had a CAA CNAME loop as described in Legacy CAA Implementation