My major problem with Traefik is that if you aren't using the defined stacks and opt for file configuration it can be a bit exhausting to configure, TOML is a rather repetitive format.
It also lacks support for HTTP streaming for non-standard HTTP (I wish there was an option to just enable streaming on a host) which sucks for some enterprise software, and streaming for entire hosts so my nextcloud instance always has to wait for the traefik host to buffer the response before being able to download the file to the browser.
However, in terms of scaling and being able to get a SSL-terminating or SSL-handover reverse proxy going it's a breeze and it handles decent load very well.
It also lacks support for HTTP streaming for non-standard HTTP (I wish there was an option to just enable streaming on a host) which sucks for some enterprise software, and streaming for entire hosts so my nextcloud instance always has to wait for the traefik host to buffer the response before being able to download the file to the browser.
However, in terms of scaling and being able to get a SSL-terminating or SSL-handover reverse proxy going it's a breeze and it handles decent load very well.