Spark 2.6.0 is frozen in the chatting windows

Dear All,

Please allow me asking you about spark 2.6.0

My server is running Openfire 3.7.0 with 100 users. All of client users are using spark 2.6.0 for communicating together. I’m facing with the issue being freezing whenever I click on user in the contact list for chatting, then it was frozen and couldn’t enter text into the window of chatting, tried to chat with another user, then it’s okay! I don’t know if it’s cause of java error or not ? I tried to update the latest version of java but it didn’t work, too. Whenever get this issue, I had to go to the path C:\Document and Setting\Myuser\Application Data\Spark\User for deleting the freezing user. Then it’s okay. But I don’t want to delete them often because I want to keep history of all users. Could you please help me find out the root of issue and fix it? I deeply thanks you very much for your help!