This isn't scientific evidence, but a possible relevant anecdote that potentially explains some of this. I had a very close friend working some kind of support role at one of the big Covid injection sites in a big US city.
I was told that at least some portion of the many nurses hired to do the vaccine injections appeared to have very little experience with that type of injection and weren't following the set procedures setup by the head doctor of the center. Because of the rushed nature of setting up the vaccination center, the hiring was rushed and the training was limited and the quality control and supervision was pretty bad.
I have a feeling that at least some of the reports of vaccine injuries may have just been caused by improper injection technique due to the rushed process.
https://pubmed.ncbi.nlm.nih.gov/34406358/