Seeing this upon application opening:

SSPI handshake failed with error code 0x8009030c, state 14 while establishing a connection with integrated security; the connection has been closed. Reason: AcceptSecurityContext failed. The Windows error code indicates the cause of failure. [CLIENT: 192.168.x.x]

Is this using integrated security instead of SQL, is that the issue?

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Have the SPNs been correctly created in Active Directory.

This may help:

SPNs in active directory 

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