The most likely reason for a timeout is this:
*) SSL_MODE_AUTO_RETRY is enabled by default. Applications that use blocking
I/O in combination with something like select() or poll() will hang. This
can be turned off again using SSL_CTX_clear_mode().
Many applications do not properly handle non-application data records, and
TLS 1.3 sends more of such records. Setting SSL_MODE_AUTO_RETRY works
around the problems in those applications, but can also break some.
It's recommended to read the manpages about SSL_read(), SSL_write(),
SSL_get_error(), SSL_shutdown(), SSL_CTX_set_mode() and
SSL_CTX_set_read_ahead() again.
Kurt
