Daylight savings time changed and NTP Servers out-of sync with ADC.
Time mismatch between client-server created by Daylight saving time 2020 began at 2:00 AM Time stamp mismatch in client-server created by Daylight Saving time change and out-of sync NTP server.
TLS is time sensitive, ADC detects a time mismatch and teardown TLS Session sending a RESET with Code 9811
Note regarding REST code 9811
As part of TLS handshake :: After a “Change Cipher Spec” message from Client machine, ADC should send back another “Change Cipher Spec” confirming the newly created TLS Session, but instead ADC sends a RESET message with RESET code :: 9811 because it detected a time stamps mismatch.
Following this article :: NetScaler Reset Error Codes
Reset code 9811 means :: NSDBG_RST_ERRHANDLER: This reset code is used with SSL. After sending a Fatal Alert, the NetScaler sends a RST packet with this error code. If the client does not display any supported ciphers to the NetScaler appliance, the appliance sends a Fatal Alert and then this RST packet.
In this case this error code is deceiving because the client machine did displayed ciphers available to ADC, but ADC found a mismatch in Time Stamp TLS Session-ID and invalidates the Session.
Cipher used on this Session was :: TLS_RSA_WITH_AES_256_CBC_SHA (0x0035)
Handshake Protocol: Server Hello
Handshake Type: Server Hello (2)
Version: TLS 1.2 (0x0303)
Session ID Length: 32
Session ID: 1a1ff2f6e4aaa45336d6c8f3454892b324fea21528474cce…
Cipher Suite: TLS_RSA_WITH_AES_256_CBC_SHA (0x0035)
Compression Method: null (0)
Extensions Length: 15
Extension: application_layer_protocol_negotiation (len=11)