TLS handshake failure from BIG-IP to backend – Fatal Alert: Decode Error (Server SSL)

Hello DevCentral Team,

I am troubleshooting a server-side TLS issue where BIG-IP intermittently fails to establish a TLS connection to a backend service.

Observed behavior:
Client to BIG-IP TLS handshake completes successfully.
BIG-IP to backend TLS handshake fails.
Backend responds with a TLS alert: Level Fatal, Description Decode Error.
Failure occurs very early in the handshake, immediately after ClientHello.

Configuration details (sanitized):
Backend service listens on HTTPS using TLS 1.2.
BIG-IP is operating in full-proxy mode.
The default serverssl profile has been removed.
A custom Server SSL profile is attached with an explicit server-name configured and server-side SNI enabled.
No client certificate authentication is required by the backend.

Validation already performed:
Direct openssl s_client testing from BIG-IP to the backend succeeds.
TLS version and cipher suites are compatible.
Backend certificate chain appears valid when tested outside BIG-IP.
The issue appears specific to BIG-IP initiated server-side TLS.

Questions:
Can a backend return a fatal decode_error even when BIG-IP sends SNI correctly?
Are there known cases where certain TLS extensions sent by BIG-IP but not by OpenSSL trigger this error?
Are there Server SSL settings commonly associated with decode_error responses?
Any recommended BIG-IP specific debugging steps beyond tcpdump and ssldump?

Thanks in advance for any guidance or similar experiences.