As you are saying that you installed it in User Mode, are you using the Service URL connection?
Try also these solutions:
Increase the UIPATH_SESSION_TIMEOUT system environment variable on your server. The default value is 60 seconds, which might be insufficient due to slow performance on some machines. Please note that the environment variable is set in Seconds and the Robot Service needs to be restarted after modifying this variable.
If the UIPATH_SESSION_TIMEOUT system environment variable value is 60 seconds, I think it’s about building the connection, not about the connection time. After the connection, it stands for at least a week.
I want to increase that connection time from minimum a week to as large as possible (to avoid the frequent log out/log in in Assistant).