When testing validation with oracle (using oracle19cRAC and ojdbc8) using the following code:

for ... iterationNum {
  OracleValidConnectionChecker or = new OracleValidConnectionChecker();             
  SQLException ex = or.isValidConnection(con);
        
  if(ex==null) System.out.println("Valid connection ...");
  else System.out.println("InValid connection ..."+ex.toString());
  sleep(time) 
}  

• when the connection to the db is fine the db connection is validated normally ....
• when the connection to the db is interrupted the invalidation message is printed normally ...
• when the network connection is re-established still there are invalidation messages ...
• when the server is restarted the db connection is validated normally again ...

When testing validation with mssql (using mssql2019 and mssql-jdbc-9.2.0.jre8) using the following code ...

for ... iterationNum {
  MSSQLValidConnectionChecker ms = new MSSQLValidConnectionChecker();
  SQLException ex = ms.isValidConnection(con);

  if(ex==null) System.out.println("Valid ms connection ...");
  else System.out.println("InValid ms connection ..." + ex.toString());
  sleep(time) 
}  

• when the connection to the db is fine the db connection is validated normally ....
• when the connection to the db is interrupted the isValidConnection method seems to get stuck ...
• most probably the previous network disconnection issue could be the same here ...