It is not easy to compromise such a system designed for high security but it might be worth it because of the high value targets. I don’t think that it’s happening now in case of Purism. So this stays theoretical here.
On the other side we have incidents like operation Rubikon which tells us how impudent state actors are and how far they might go.
Also I always thought that the Snowden revelations were not only an event causing several messengers to be born which calling themselves secure. It also would have been a good point in time for intelligence services to create an own pseudo secure messenger as honeypot. Just a thought. I have no solid indicators in that direction. So this is speculation.