A couple of slight mischaracterisations, perhaps. These were not serious adverse reactions they were serious adverse events (SAE's) - there's a difference. For instance some of the adverse events were totally accidental occurrences like broken limbs that just happened to occur in trial participants.
Also the 3 you mention were not believed to be linked to "the" vaccine, they were possibly linked to "a" vaccine. One of the SAE's was in a person who received the MenACWY vaccine, not the Covid vaccine and one was in a volunteer who is still masked as to group allocation (so it's not known if they received the Covid vaccine or not).
It's also worth mentioning that subsequent to their SAE's, according to the Lancet paper, "All trial participants have recovered, or are in a stable or improving condition."