mRNA breaks down quickly. The whole complication of mRNA based vaccinations was the delivery system: to ensure it wouldn't be destroyed before causing an immune response.
The question scientists are having is more about how long the effect lasts and ensuring that the mRNA doesn't break down before it is used.
Our bodies deal with faulty DNA and RNA and foreign genetic materials all the time.
Prions are a very serious and rare disorder. Anyway, even if the vaccinations cause prion diseases, that means that about half the population in the USA is doomed.
But, beware of just linking studies and speculation based on keywords.
It is like saying WiFi transmissions can cook you just because they usually use the same frequency as microwave ovens (2.4 GHz). One needs to have a relevant background to interpret studies properly.
Otherwise, it is just keyword fear mongering.
I prefer to think: what is more likely? That greedy, selfish, and power hungry people will kill 70% of the population when their goals require people to be around to give the money? Or that they did their best to make a product that will work and increase their shareholder value and profits?
The question about these vaccines they are asking is if they last more than 6 months, not whether they last forever.