This is possible, but I work in medical research, and this pause is pretty standard practice. When there is a potential problem, you pause, gather more data, come up with a mitigation plan (if needed) and submit all this to the ethics authority (usually IRB). Its rote standard practice. And i think much more likely that they are following standard practice than there are hidden issues that haven't otherwise been revealed publicly yet.

That said, this is not a usual situation at all, and I think it's absurd, not least because of lives potentially saved during this pause, but because of the carry on effects with vaccine hesitancy, etc.