You may encountered issues while using Traefik so giving your opinion is totally fine, but I don't think that's fair to overreact.
Many users (and I mean big companies) have been using Traefik in production for years without issue. I'm not saying there is not bug, which software can claim this, I'm just saying that many users have a good opinion on Traefik stability.
We follow semver, there shouldn't be any breaking change between 2 minor versions. But, yes, it can happen, sometimes, we may have forgot to check a specific use case. But hey, again, let's be fair, we don't want it. We are just human. And no, this does not happen at every minor version and this is pretty uncommon...
Finally, on Traefik size. You are including Traefik dependencies, in vendor/, which is a bit weird. In go, the convention is to push the dependencies in your repository to get reproducible builds, so that's not a good way to count. If you exclude vendor/:
golocc --no-vendor ./...
Lines of Code: 58532 (2987 CLOC, 55545 NCLOC)
Which is rather tiny.
So all in all, I regret you had such a bad experience with Traefik, but I just wanted to express the fact that many users are using it without any issue :) I would be happy to discuss further on this.
Fabio might be a good alternative, but we don't need Consul right now, so I don't want to have to manage yet another puzzle piece.
Should I go with nginx?
As you mentioned, the docs are terrible. What makes that worse are the undocumented breaking changes between each release. They don't even pretend to follow semver, so v1.5 broke v1.4, and v1.6 broke v1.5. Each update you pray that it doesn't take your whole setup down. If anything goes wrong, since nothing is documented and there's often no logs explaining what went wrong, you might be down for an extended period while you make 100 best-guess changes to the config that worked in staging, but for whatever reason isn't working in production. May the odds be ever in your favor.
Last I checked, Traefik was 988,000 (!!!) lines of code. That's 20x the size of my very complex web application. I replaced it with 500 lines of go providing all the essential features for me. Higher reliability, way fewer bugs, no breaking changes.