Spark locks up when connecting to certain user

Hi, one of my users running Spark 2.5.8 is getting locked up only when she tries to message one certain contact. The program must be closed using the Task Manager. All other contacts can be accessed. Things I’ve tried:

Re-install Spark - also deleting Spark profile folder

Deleting and recreating user on Openfire server.

Still the problem persists. Any help would be appreciated.

Thanks

Tim