There is a known issue with SQL Prompt and SSMS versions 18.0 to 18.4, which can cause error messages similar to this to appear:

Could not load file or assembly 'Microsoft.SqlServer.ConnectionInfo, Version=16.100.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91' or one of its dependencies. The system cannot find the file specified. (RedGate.SharedSSMS.2018)

To fix this issue please upgrade SSMS to version 18.5 or later.