This post, a day before yours on the lemmy_support@lemmy.ml community, is describing some similar behavior, with some CPU usage at start (at least on the first boot; not clear whether that is a one-off on migration from the text) and then federation problems with 0.19.1:
After upgrading Lemmy from 0.18.5 to 0.19.1, the lemmy_server process is taking up 200-350+% of my CPU…It seems like my instance isn’t federating properly now tho.