if I were writing stories about the gov "firing thousands of probationary workers" I would probably rewrite as "firing thousands of new hires or people new to their role because of promotion or transfer -- who are often on a status called "probation" --" because I think the general understanding of "probation" is "in trouble for something they did"
if I were uncharitable, I'd think the usage of "probation" without the qualifier first was the result of unexamined regurgitation of a press release