You can fish in lava

Please provide more details regarding this problem. Is the issue that you can't catch fish in lava, or that the fishing bobber doesn't get destroyed in lava?

You can't catch fish, and I don't exactly know if the bobber gets destroyed in lava. The black string still appears.

I went into spectator mode, and this is what I saw.

Note: my head is in the lava.

In that case, this ticket is a duplicate of MC-176926, which was later resolved as invalid due to being a feature request.