If the recorder isn't recording because it thinks you're on a call, you might try going into the recorder app settings and removing phone permission because, along the lines of what mustang7757 was saying, I've heard Google blocked call recordings in Pie. I honestly haven't confirmed this but from what I've been seeing it seems to stand up. So if it thinks the app has phone permission it may be blocking its use or causing problems.
Meanwhile take advantage of the link provided to offer a but more info and we'll do what we can to offer you the best advice.