They never supported Bernie’s policies. It wasn’t very many, but there were a bunch of Bernie Bros in 2016 who switched from him to Libertarian candidate Gary Johnson. There is very little policy overlap between the two aside from being contrarian. That’s all they were doing: being contrarian without any actual policy ideas.

However, the vast majority of Bernie primary voters did vote for Hillary that year.

there were a bunch of Bernie Bros in 2016 who switched from him to Libertarian candidate Gary Johnson. There is very little policy overlap between the two aside from being contrarian

Only if you insist on viewing politics through a left-right axis and ignore the authoritarian-libertarian axis. Or if you’re weirdly using “contrarian” as a synonym for “not authoritarian,” which I guess makes sense.

The political compass is an only slightly better model than the one that’s based on 18th century French parliament seating arrangements.
Nevertheless, it does expose a commonality between Sanders and Johnson that you denied.

It’s still jumping between a left-right axis while staying on the libertarian-authoritarian axis. It shows you were never grounded on that axis in the first place.

A better way to think about political affiliations is a big graph of nodes connected by edges. The downside is that your political map will end up looking like an Always Sunny meme. However, it’s a really powerful tool that explains what Horseshoe Theory is getting at without trying to contort the whole thing.