I had very bad experience reinstalling tor because of libevent and I would like to share my experience.
Tor stopped working because of v2 addresses. I unistalled it. When reinstalling, it could not find installation candidate for Ubuntu Bionic until I enabled universe repository. Then it installed, but did not start hidden service. When starting tor manually, it was still complaining about missing libevent. No guide on the net helped, reinstalling libevent always installed newer version than tor was looking for.
I had to solve things in the strange way. It looks like when I uninstalled tor v2 the libevent-2.1.so.6 got wiped out. Probably by my other actions. When I reinstalled tor and I was trying to reinstall libevent, other versions were installed, like libevent-2.2.so.1, but tor was still complaining about missing libevent-2.1.so.6. Fortunately I found it in old backup and I just copied it to /usr/lib/x86_64-linux-gnu/. The tor from the command line started to work, but it did not work as a service. I think I fixed that by changing owner of hidden_service directory to debian-tor. Then service started to work after I restarted computer. Hope this will help someone, it took me four evenings to fix.