LTA error: "Cannot invoke object with invocation handler in this context"

[zoffixznet]

I did some work on synopsebot and now when I try to start it I get:

git clone https://github.com/perl6/synopsebot
cd synopsebot
git checkout f3398f96bb97ad3
./dev-start-localhost 

# say R#1000 on the channel the bot joined

[...]
Cannot invoke object with invocation handler in this context
  in block  at /home/zoffix/rakudo/install/share/perl6/site/sources/9F9667E70A5096626056EBEF3FAD8C9345F106CC (IRC::Client) line 111
[...]


$ perl6 -v
This is Rakudo version 2018.05-54-g148d7c5 built on MoarVM version 2018.05-57-g89dee3b
implementing Perl 6.c.

The error is insufficient for me to even guess at what the problem might be.