Websocket fails with cro-websocket >0.8.7 on ping

[maros]

Mar 06 12:27:21 statusapps werdad[3889262]: Mattermost WebSocket is gone. Reconnecting
Mar 06 12:27:22 statusapps werdad[3889262]: Invocant of method 'unlock' must be an object instance of type 'Lock',
                                            not a type object of type 'Lock'. Did you forget a '.new'?
                                              in block  at /opt/rakudo-pkg/share/perl6/site/sources/45334C557865A97D1ECA0D3F3A3FAF2017FCE553 line 30
                                              in block  at /opt/rakudo-pkg/share/perl6/site/sources/45334C557865A97D1ECA0D3F3A3FAF2017FCE553 line 25
                                              in method ping at /opt/rakudo-pkg/share/perl6/site/sources/43B45024F925BC97E4E6FB16AA646E0F82BFA422 line 174
                                              in block  at /opt/gh/geizhals-werda/service.p6 line 67

45334C557865A97D1ECA0D3F3A3FAF2017FCE553 is MetamodelX::MonitorHOW
43B45024F925BC97E4E6FB16AA646E0F82BFA422 is X::Cro::WebSocket::Client::Closed

Caller code is

    # Start main websocket loop
    start react {
        whenever Supply.interval(60,10) {
            if ($connection && ! $connection.closed) {
                await $connection.ping(timeout => 1); # this line causes the exception

                CATCH {
                    default {
                        $log.error('Mattermost WebSocket is gone. Reconnecting');
                        $log.warn(.gist);
                        connect();
                    }
                }
            } else {
                connect();
            }
        }
    }

Downgrade to 0.8.6 mitgates the issue.