> There's not really a plausible mechanism that could cause problems to happen long after the fact.

Well there are some limited circumstances, but I don’t think they justify not going forward with the vaccine. For instance there is a possibility in some individuals that the mRNA itself (not just the spike protein) as well as the lipid encasing it to protect it and transport it into the cell can cause an immune response. It’s theoretically possible that in some individuals that could result in auto immune responses to other forms of messenger RNA in their cells. [1]

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5906799/

From the article

“A possible concern could be that some mRNA-based vaccine platforms induce potent type I interferon responses, which have been associated not only with inflammation but also potentially with autoimmunity”