Dell Wyse 3040 thin client - Citrix Applications are freezing

Users are facing issues with this thin client where after the log in they launch Citrix applications and the application is freezing while they are typing and it is stuck.

This is happening to several thin client users. Dell, can you explain why this could be happening? I am new to this Thin Client. Our environment is XenApp 6.5.

Please, there are several users affected, and I am not sure whether we even have support.

Thanks in advance! I appreciate if anyone could let me know so I can fix for the customers. The guys who know this are on vacation and I cannot help as I am not aware of anything.