SOLVED: The problem was specific to the Safari web browser and was fixed in unRAID 6.5.1-rc6.   I'm getting a series of nginx-related error messages in my syslog that I've never seen before: Mar 25 19:23:49 Northolt nginx: 2018/03/25 19:23:49 [crit] 7004#7004: ngx_slab_alloc() failed: no memory Mar 25 19:23:49 Northolt nginx: 2018/03/25 19:23:49 [error] 7004#7004: shpool alloc failed Mar 25 19:23:49 Northolt nginx: 2018/03/25 19:23:49 [error] 7004#7004: nchan: Out of shared memory