IMO, this is a problem that very few people like to talk about, because we all subscribe to the (correct) idea that a good developer should be tech agnostic. Sadly, those in charge of hiring don't seem to believe the same thing.

I was in a somewhat similar boat. I was a .NET developer that wanted to try something new, and despite eight years of experience few people wanted to take a chance on someone. I managed to find a role doing Ruby, and I've managed to transition to a new stack and language fairly well.

The only roles where I had any real bite were the ones where I applied directly, and where the person on the other end of the table from me was a developer. To highlight the issue, the second I had Ruby on my CV after taking this role, the same companies that wouldn't hire me for a mid-level role wanted to offer me an interview for senior-level roles...