Don't get intellisense due to login error. Why?

I get intellisense for every other server in the enterprise, except for this one. The SqlPrompt/Help/Show Log menu yields the error below.

I can login to the box fine in SSMS and can run queries no problem. The only issue is that there is no intellisense.
What am I missing here?

SQL Server version: Microsoft SQL Server 2017 (RTM) - 14.0.1000.169 (X64) Aug 22 2017 17:04:49 Copyright (C) 2017 Microsoft Corporation Enterprise Edition: Core-based Licensing (64-bit) on Windows Server 2016 Datacenter 10.0 <X64> (Build 14393: ) (Hypervisor)

SQL Prompt Version: 8.0.7.1917

The interesting thing is that if I remove the port number from the connection string, it functions correctly.

09 Jan 2018 22:30:48,959 [41] WARN  RedGate.SqlPrompt.Cache.Candidates.ServerCandidate - Failed to load server RWX-SQL-OC2-P1A\RWXSQLOC2P1,50561
System.Data.SqlClient.SqlException (0x80131904): A connection was successfully established with the server, but then an error occurred during the login process. (provider: SSL Provider, error: 0 - The certificate chain was issued by an authority that is not trusted.) ---> System.ComponentModel.Win32Exception (0x80004005): The certificate chain was issued by an authority that is not trusted
   at System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity, SqlConnectionString connectionOptions, SqlCredential credential, Object providerInfo, String newPassword, SecureString newSecurePassword, Boolean redirectedUserInstance, SqlConnectionString userConnectionOptions, SessionData reconnectSessionData, DbConnectionPool pool, String accessToken, Boolean applyTransientFaultHandling)
   at System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection, DbConnectionOptions userOptions)
   at System.Data.ProviderBase.DbConnectionFactory.CreateNonPooledConnection(DbConnection owningConnection, DbConnectionPoolGroup poolGroup, DbConnectionOptions userOptions)
   at System.Data.ProviderBase.DbConnectionFactory.TryGetConnection(DbConnection owningConnection, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, DbConnectionInternal& connection)
   at System.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions)
   at System.Data.ProviderBase.DbConnectionClosed.TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions)
   at System.Data.SqlClient.SqlConnection.TryOpenInner(TaskCompletionSource`1 retry)
   at System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry)
   at System.Data.SqlClient.SqlConnection.Open()
   at RedGate.SqlPrompt.Cache.Candidates.ServerCandidate.IsContainedOrRestrictedDatabase(ConnectionProperties cp)
   at RedGate.SqlPrompt.Cache.Candidates.ServerCandidate.LoadDatabaseContainment()
   at RedGate.SqlPrompt.Cache.Candidates.ServerCandidate.LoadServer()
ClientConnectionId:6e51940f-27d2-4328-b3b2-c552fe7dc730
Error Number:-2146893019,State:0,Class:20