Yes, there were layoffs. But "core maintainers" is not a term they use, and kind of fuzzy since people come and go; some early team members left well before then. People didn't all leave (or get laid off) at the same time, and they never laid off the entire team as far as I know.
More:
https://www.reddit.com/r/FlutterDev/comments/1cduhra/comment...