This is the first time I hear this sort of problem.
Which version of the xUML Runtime do you use?
Do you use old SAP or SAP NW library?
In case of an communication you should get this error:
[SAPADLM][An error occurred while waiting for an SAP request. Will retry in 60 seconds.
And it should automatically reconnect.
Do you get errors in the log file?
At last resort you can restart the service.