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Re:An introduction to RabbitMQ by ramchip on Thursday May 21, 2020 @04:37PM (#23264842)
Erlang/OTP-22 (released last year) introduced TLS distribution optimizations and message fragmentation which sound very related to the problem you saw:

http://blog.erlang.org/OTP-22-Highlights/

The fragmentation in particular addresses the problem where a large message would block all other messages, including heartbeats, and cause nodes to look “down” when they’re not.

Re:An introduction to RabbitMQ by shoo on Thursday May 21, 2020 @05:03PM (#23265300)
fantastic. thank you for sharing that -- my anecdote about this problem is slightly dated -- it would have been late 2017 early 2018 we were seeing the issue, which indeed predates OTP 22 release.