HELO::ReportUnitUsage leads to the server disconnecting

For MB-53127 it's been recommended we try the new HELO::ReportUnitUsage feature to find out what RUs and WUs we're using under Elixir.

However this is leading to the server disconnecting on me when I try to do a sub-doc mutate.  My test is just connecting to the cluster and doing a single transaction.  If I disable the ReportUnitUsage negotiation, the test passes fine.

I followed the Elixir self-serve instructions here https://hub.internal.couchbase.com/confluence/pages/viewpage.action?spaceKey=PM&title=Elixir+Self-Service+Demo+Instructions

Since this is Elixir I'm not sure what other info I can provide, e.g. no access to cbcollect or server logs AFAIK.

As an extra data point: I also tried the same test against Morpheus 8.0 build 1083.  The test passes fine, but no RUs and WUs are returned in the flexible extras.  I wasn't really expecting it to since it's not Elixir, just mentioning that this server build doesn't disconnect (but perhaps because internally it will be skipping the RU/WU-returning code).