More update:
I've discovered that when locking down the ciphers etc you need to be careful. The symptom I experienced was:
Logs & Monitors > General Overview or new tab "Error loading tab - Error: SslVersionOrCipherMismatch" Gateway object license tab "Loading Error: ERRL_SSL_VERSION_OR_CIPHER_MISMATCH" for more details see sk166932.
I check the KB and found SK171707, after which then lead me to the lockdown I did. At this point I tweaked the setting to the following:
SLCipherSuite HIGH:!ADH:!RC4:!DHE:!LOW:!EXP:!RSA:!eNULL:!aNULL:!SSLv2:!MD5
SSLProtocol -ALL {ifcmp = $httpd:ssl3_enabled 1}+{else}-{endif}TLSv1.1 +TLSv1.2 +TLSv1.3
When run a scan against the IP for the SMS I get the following discovered:
SLCipherSuite HIGH:!ADH:!RC4:!DHE:!LOW:!EXP:!RSA:!eNULL:!aNULL:!SSLv2:!MD5
SSLProtocol -ALL {ifcmp = $httpd:ssl3_enabled 1}+{else}-{endif}TLSv1.1 +TLSv1.2 +TLSv1.3
When run a scan against the IP for the SMS I get the following discovered:
TLSv1.3 enabled
TLS Fallback SCSV:
Server supports TLS Fallback SCSV
TLS renegotiation:
Session renegotiation not supported
TLS Compression:
Compression disabled
Heartbleed:
TLSv1.3 not vulnerable to heartbleed
TLSv1.2 not vulnerable to heartbleed
Supported Server Cipher(s):
Preferred TLSv1.3 128 bits TLS_AES_128_GCM_SHA256 Curve 25519 DHE 253
Accepted TLSv1.3 256 bits TLS_AES_256_GCM_SHA384 Curve 25519 DHE 253
Accepted TLSv1.3 256 bits TLS_CHACHA20_POLY1305_SHA256 Curve 25519 DHE 253
Preferred TLSv1.2 256 bits ECDHE-RSA-AES256-GCM-SHA384 Curve 25519 DHE 253
Accepted TLSv1.2 256 bits ECDHE-RSA-CHACHA20-POLY1305 Curve 25519 DHE 253
Accepted TLSv1.2 256 bits ECDHE-ARIA256-GCM-SHA384 Curve 25519 DHE 253
Accepted TLSv1.2 128 bits ECDHE-RSA-AES128-GCM-SHA256 Curve 25519 DHE 253
Accepted TLSv1.2 128 bits ECDHE-ARIA128-GCM-SHA256 Curve 25519 DHE 253
Accepted TLSv1.2 256 bits ECDHE-RSA-AES256-SHA384 Curve 25519 DHE 253
Accepted TLSv1.2 256 bits ECDHE-RSA-CAMELLIA256-SHA384 Curve 25519 DHE 253
Accepted TLSv1.2 128 bits ECDHE-RSA-AES128-SHA256 Curve 25519 DHE 253
Accepted TLSv1.2 128 bits ECDHE-RSA-CAMELLIA128-SHA256 Curve 25519 DHE 253
Accepted TLSv1.2 256 bits ECDHE-RSA-AES256-SHA Curve 25519 DHE 253
Accepted TLSv1.2 128 bits ECDHE-RSA-AES128-SHA Curve 25519 DHE 253
Server Key Exchange Group(s):
TLSv1.3 128 bits secp256r1 (NIST P-256)
TLSv1.3 192 bits secp384r1 (NIST P-384)
TLSv1.3 260 bits secp521r1 (NIST P-521)
TLSv1.3 128 bits x25519
TLSv1.3 224 bits x448
TLSv1.2 128 bits secp256r1 (NIST P-256)
TLSv1.2 192 bits secp384r1 (NIST P-384)
TLSv1.2 260 bits secp521r1 (NIST P-521)
TLSv1.2 128 bits x25519
TLSv1.2 224 bits x448
Issue was resolved in the GUI.
If anyone can suggest further tweaking please shout, as I would like to lock this down much as possible.