Hello,
Yes, unfortunately there is a bug with ETR Madara that will sometimes freeze the client when his mystery is used. The devs are aware of this, but it has been a persistent issue in some game modes (such as team instances). I will submit a bug report to them about this on your behalf to bump the issue, but for now all I can offer a workaround—avoiding using ETR's splash mystery or some of the more powerful splash mechanics should prevent this issue, especially against clones/puppets.
Thanks and have a great day!