nil @current_selector causing HTTP2::Error::ProtocolError

Unfortunately, I do not have a very good error report, it's been captured a few times by our error tracker without a full stacktrace. It looks like it came from this line: https://gitlab.com/os85/httpx/-/blob/41661a05c3b5346bab73315dd3a17ace340778fe/lib/httpx/connection.rb#L943

This is pretty much all the information we captured:

HTTP2::Error::ProtocolError
undefined method `after' for nil:NilClass (HTTP2::Error::ProtocolError)

NoMethodError
undefined method `after' for nil:NilClass (NoMethodError)

        timer = @current_selector.after(timeout, callback)
                                 ^^^^^^

We're running version 1.6.2 of httpx, and version 1.1.1 of http-2.

Not sure if this indicates that there is a bug in httpx or http-2, or if the server we were connecting to was having http2 protocol issues?