DTLS session resumption; frequent "Can't interleave application and handshake data" errors #4782
Description
When my DTLS client connects to the server over a certain distance/latency (around 100-200ms latency) I have found the above error occurs a lot, but only when session resumption is enabled and not always. It can go through periods where repeated handshakes fail in this manner, and other times when it works just fine.
With session resumption disabled (by overriding tls_should_persist_resumption_information to return false), the issue apparently disappears completely, and the full handshake succeeds.
At first I thought I was simply seeing this issue #2498 but it turns out on closer inspection that neither the client or server are retransmitting anything during these failed handshakes.
Both client and server use the Botan DTLS implementation from version 3.6.1.