Is anyone able to clarify 'missing trie node' issue for me?

I just came across Ankr nodes and noticed that the free tier plan is able to support archive nodes, great! One issue, when I try to use one of the free endpoints to fetch archival data, I get an error code with 'missing trie node' followed by a string of characters and (path). from what I can tell here: https://ethereum.stackexchange.com/questions/39610/missing-trie-node-when-requesting-balance it would seem that this error is caused by the data not actually being present, so not actually an archive node. Is anyone able to clarify this issue for me?