I think there may be a problem in the shared memory implementation. I'll look into that. In the meantime, you have several choices. First, you can force a TCP-IP implementation with the -host option or the -port option. Second you can have users click on the "new-ish" Rescan this button in the AFNI GUI. Third, you can set the AFNI environment variables, AFNI_RESCAN_AT_SWITCH or AFNI_AUTO_RESCAN, in the .afnirc to force a rescan either when a user clicks on Switch Underlay/Overlay or every 15 seconds, respectively.